One should be aware that although the imam’s names, especially Imam Ali’s, haven’t been mentioned in the Quran, nevertheless, their names, especially Imam Ali’s, can be found in the Prophet’s sayings.
One very good example is the hadith of Ghadir which is considered the official announcement of the appointment of Imam Ali as successor to Prophet Muhammad (p.b.u.h.) after his decease. This hadith sanad wise (its chain of narrators) is mutawatir (meaning that the number of narrators narrating it is so high that one becomes sure that the hadith is authentic and that all of the narrators can’t be lying or can’t be mistaken in their narration), and concerning its content and meaning, contains clear evidence on Imam Ali (a.s.) being Imam.
To answer this question, First of all, one must note that: 1- The imams’ names have been explicitly mentioned in the Prophet’s sayings, especially Imam Ali’s name in which the Holy Prophet of Islam has in many different events, clearly stated that Imam Ali is his successor and the religious authority after him. For example, in the wake of Prophet Muhammad’s prophethood, when he was ordered by Allah to invite his tribe, family, and relatives to Islam, he declared: “The first person to believe in me (answer my call to Islam) will be my wasiyy, minister, and successor.” The only person to answer him was Imam Ali (a.s.). In the end, when no one answered the Prophet other than Ali (a.s.), he said: “After me, you (Ali) are my wasiyy, minister and successor.” Another example is the famous hadith of Ghadir in which the Prophet clearly stated that: “Whosoever I am his Mowla, Ali is his Mowla.” Also in the hadith of Manzilah, the Prophet states that: “You (Ali (a.s.)) are in comparison with me, like Harun compared with Musa, the only difference (between us and them) is that there is no prophet after me.” The hadiths of the holy Prophet (p.b.u.h.) regarding the fact that Imam Ali (a.s.) will take his place are mostly Mutawatir (meaning that there is no doubt that the hadith has been said by the prophet because the number of narrators is so high that one becomes sure that it is impossible for the hadith to be an unauthentic one) and this fact has been pointed to in both Sunni and Shia books. In yet another hadith, the Prophet (p.b.u.h.) names all of the imams after him for Jaber-ibn-Abdillah-al-Ansari, from Imam Ali until the twelfth and final imam meaning Imam Mahdi (a.s.).
So one should be aware that although the imams’ names haven’t been explicitly stated in the Quran, yet the holy Prophet, whose words are all true and come from Wahy (divine inspiration), has clearly expressed their names and emphasized on their being imams after him.
2- Imam Ali’s Wilayah (religious authority) has been pointed out in the Quran even though his name hasn’t been explicitly mentioned. Both Shia and Sunni commentators of the Quran admit that verse 55 of surah Ma’idah has been revealed regarding Imam Ali (a.s.) and that he is the only one meant by it. “Only Allah is your waliyy and His apostle and those who believe – those who establish salat and give charity while bowing (in rokoo’).”
Given the fact that in Islam there is no ruling saying that giving charity while in rokoo’ (bowing in prayer) is preferred as mustahabb or wajib, one can easily conclude that this verse is pointing to an event that occurred only once. This verse is speaking of the time in which Imam Ali was praying in the masjid. When he went down to rokoo’, a beggar came up to him asking for help, Imam Ali pointed to his finger and the beggar approached him, took off the imam’s ring and left. Thus, the verse is saying that religious authority and supervision of the Islamic ummah are solely for Allah, His messenger and Imam Ali (a.s.), and other than them, no one has any authority.
So, till now we have concluded that the imams’ names have been mentioned by the Prophet (p.b.u.h.) and Imam Ali’s wilayah has clearly been pointed to in the Quran, such that an unprejudiced and unbiased researcher really searching for the truth, can easily reach the conclusion that the Prophet’s (p.b.u.h.) standpoint on those succeeding him, was that Imam Ali (a.s.) and his children are to succeed him after his passing away. But why haven’t Imam Ali and the other imam’s names been explicitly mentioned in the Quran? There can be two reasons behind this issue:
1- “The Quran usually speaks in a very general way and mostly teaches us principles, ways and methods (instead of getting very specific) as it has regarding the osool (pillars)and foroo’ (branches) of Islam.” This is what Imam Sadeq (a.s.) has said. He goes on to give us three examples: a) Salat. The Quran has been general regarding salat; not being specific about how long it is supposed to be and how it is supposed to be performed. On the other hand, the Prophet of Islam (p.b.u.h.) has clearly illustrated how to perform it for us and how many rak’ats each prayer should be. b) Zakat. In the Quran, zakat has only been mentioned as an Islamic ruling. It was the Prophet who expressed which things have zakat and what the criteria for zakat becoming wajib for each one is.
- c) The Quran says that Hajj is wajib and no more, but the Prophet has explained how it is supposed to be performed.
Therefore, it is wrong to expect to be able to find every detail in the Quran. So it is a big mistake not to follow the imams just because of the fact that none of their names have come in the Quran. That’s why no one says that noon prayers (which are 4 rak’ats) have to be prayed 2 rak’ats just because the Quran hasn’t mentioned how many rak’ats each prayer is.
2- In issues like this, in which there are big chances that others will disagree, it is much better for the Quran to express the truth implicitly rather than explicitly, otherwise there is a high possibility that they will end up denying the Quran as a whole. It’s very obvious that such a problem isn’t to the benefit of the Muslim ummah. Of course, the Quran says: “Surely we have revealed the Reminder (the Quran), and We will most surely be its guardian”, but one should remember that one of the ways of protecting the Quran and not letting others falsify or change it, is for it to speak in a way that others (such as the hypocrites who show that they are Muslims on the outside even though they aren’t within) don’t get sensitive and provoked. In this way, the high respect and value of the Quran will be kept, and certain individuals won’t think of changing or falsifying it in a way that will comply with their personal desires and wicked goals or just because they disagree with something.
Shahid Ayatollah Motahhari answers this question in the following way. He says: “The answer to the question that why hasn’t Imam Ali’s khilafah and imamah been mentioned in the Quran, is that 1- The Quran usually expresses general laws. 2- The Holy Prophet (p.b.u.h.) or Allah (s.w.t.) didn’t want such an issue in which people are sensitive about and prefer their own desires (to what Islam wants), to be presented explicitly, and although it wasn’t, people still went against it and falsely interpreted the Prophet’s sayings to their own benefit. In other words even if the Quran had clearly stated that Ali (a.s.) is successor to the Prophet they still would have found a way around it. The holy Prophet (p.b.u.h.) said: “ذا علی مولاه” (Ali is his Mawla). How much more clear can one get? (Yet they interpreted what he said falsely and according to their will.)Yet there is a big difference between ignoring what the Prophet (p.b.u.h.) has said after him passing away regardless of all of its clarity and ignoring what the Quran has been completely clear about one day after his demise. That is why I have narrated in my book “Khilafah and Wilayah” that once during Imam Ali’s reign, a Jew wanted to attack and criticize the Muslim ummah for undesirable events that took place in the beginning of Islam. He told Imam Ali (a.s.) (and of course what he said really was a negative point) that you (the Muslim ummah) started quarreling over your prophet even before completely burying him after his death. Imam Ali answered: We argued about what he had instructed, not over the Prophet himself, but you (meaning the Jews) disregarded the most important principle of your religion which is tawhid (oneness of God), and asked your prophet to build an idol for you to worship. So there is a big difference between you and us; we didn’t argue about our prophet, we argued about what the interpretation of his saying was (and what he wanted us to do after his death). These two vary tremendously. (Motahhari goes on to say that) there is a big difference between saying that the people back then had misunderstood what the Prophet had said and saying that the Muslims back then rejected what the Quran had clearly stated or had falsified it.
So one can say that the main reason behind not mentioning the names of the imams, or at least Imam Ali’s name, is the protection of the Quran from falsification and change, and that is why the verses of tathir, tabligh, and wilayah are all located between verses that are either talking about the Prophet’s wives, different Islamic rulings, or not being friends with The People of the Book (ahlul-kitab), which all have nothing to do with the religious authority of the imams and Imam Ali (a.s.), yet the fair and unbiased researcher can with the least consideration tell that this part of the verse is separate from the verses before and after it and is located there for a certain reason.
 Ibn-al Bitriq, Al-Umdah, pg.121 & 133, Seyyed Hashem Bahrani, Ghayat-ul-Maram, pg. 320, Allamah Amini, Al-Ghadir, v.2, pg. 278.
 This hadith is mutawatir (a hadith that has been narrated so many times by different narrators that one becomes sure that it is authentic) and has been narrated in both Shia and Sunni books. In the book Al-Ghadir, the different “levels of narrators” of the hadith from the first till the fourteenth century (lunar calendar) have been named, in which the foremost are more than 60 narrators from the Prophet’s companions who have narrated the hadith in Sunni books and whose names have been recorded there. Also, in Mir Hamed Hosein’s book, Abaqat, it has been proven that this hadith is mutawatir. See Al-Ghadir, v.1, pg.14-114, Ibn-al-Maghazeli, Managheb, pg. 25-26, Motahhari, Emamat va Rahbari, pg. 72-73.
 Al-Umdah, pg.173-175, Ahmad-ibn-Hanbal, Musnad Hanbal, v. 3, pg.32, Al-Ghadir, v.1, pg. 51, v.3, pg. 197-201.
 Many efforts have been made in both Al-Ghadir and Abaqat to prove that the traditions concerning Imam Ali’s imamah are mutawatir. Fazel-e-Qooshji, a Sunni scholar, doesn’t reject the fact that some of these traditions are mutawatir. See Sharh-e-Qooshji bar Tajrid-ul-I’tiqad, Khajeh al-Tusi.
 Muhammad-ibn-Hasan al-Ameli, Ithbat-ul-Hudat, v.3, pg. 123, Suleiman-ibn-Qandoozi, Yanabee’-ul-Mawaddah, pg. 494, Ghayat-ul-Maram, v.10, pg. 267 (as quoted by Misbah Yazdi, Amoozesh Aqa’ed, v.2, pg. 185).
 “Nor does he (The Prophet (p.b.u.h.)) speak out of desire, It (what he says) is nothing but divine revelation (from Allah (s.w.t.))” Najm:3-4
 See tafsir books, commentaries regarding this verse, such as Fakhr-ul-Din Al-Razi, Al-Tafsir-ul-Kabir, v.12, pg. 25, Tafsir Nemooneh, v.4, pg. 421-430, Jalal-ul-Din Al-Suyuti, Al-Durr-ul-Manthoor, v.2, pg. 393. Also, Sunni hadith references have narrated the hadith; Muhibb-ul-Din Tabari, Thakha’ir-ul-Uqba, pg. 88, Jalal-ul-din Suyuti, Lubab-ul-Nuqul, pg.90, Ala’ul-Din Ali Al-Muttaqi, Kanz-ul-Ummal, v.6, pg. 391, and many other references in which Tafsir Nemooneh has pointed to some of them.
 This analysis has been acquired from Shahid Motahhari’s book Emamat va Rahbari, pg. 37.
 According to Arabic literature scholars, the word “innama” means “only” and shows that what has been stated in the sentence is something exclusively for the person(s) mentioned.
 Koleini, Osool-ul-Kafi, kitab-ul-hujjah, v.1, chapter Ma nassallahu wa rasuluhu alal-a’immah wahedan fawahedan.
 This is the hadith itself:
عن ابى بصیر قال: سالت اباعبدالله (ع) عن قوله الله عزوجل “اطیعوا الله و اطیعوا الرسول و اولى الامر منکم”، فقال (ع) نزلت فى على بن ابى طالب و الحسن و الحسین فقلت له: انّ الناس یقولون: فما له لم یسم علیا و اهل بیته فى کتاب الله عزوجل ؟ قال (ع) قولوا لهم: ان رسول الله نزلت علیه الصلاة و لم یسم الله لهم ثلاثاً و اربعا، حتى کان رسول الله هو الذى فسر لهم ذلک .و نزلت علیه الزکاة و لم یسم لهم من کل اربعین درهماً، حتى کان رسول الله هو الذى فسر لهم ذلک .و نزل الحج فلم یقل لهم طوفوا اسبوعاً حتى کان رسول الله هو الذى فسر لهم ذلک.
 This point was mentioned by Ayatollah Hadavi Tehrani in his classes of The Theological Principles of Ijtihad, which will be printed in the second volume of The Theological Principles of Ijtihad.
 Emamat va Rahbari, pg.109-110, 27th edition, Sadra Press, Tehran, 1381.
 “Verily, Allah’s will is to remove all impurity from you, ye household (of the Prophet) and to purify you thoroughly.” This part of the verse has been placed between verse speaking about the wives of the Prophet (p.b.u.h.). Ahzab:33
 “O Messenger! Proclaim the (message) which hath been sent to thee from thy Lord. If thou didst not, thou wouldst not have fulfilled and proclaimed His mission” This verse is in between verses speaking about haram meat and animal corpses (which are haram). Ma’idah:67
 “Verily your Waliyy is Allah and…” which is located after verses regarding not being friends with the Christians and Jews. Maidah:55
 This was also pointed to in one of Ayatollah Hadavi’s classes on the theological principles of ijtihad which will be printed in the second volume of the book.