It is obligatory on a person who is sane, mature, needless and conscience at the Maghrib of the night of Eid al-Fitr, to pay three kilograms of his or her dominant daily food (usually the most important dominant food at the moment is wheat or rice) or its equivalent in cash to the poor as a religious tax.
The time for paying Fitreyyah is from the Maghrib of the night of Eid al-Fitr until before the Eid al-Fitr prayer. If it is not possible to pay it at this time, it is obligatory for him or her pay it to the poor whenever possible by the intention of nearness to Allah and without the intention of Ada or Qadha.
The reference should be Sādāt if the payee is Sādāt and Non-Sādāt if the payee is Non-Sādāt.
Ayatollah Khamenei’s Fatwa on this Issue
The Grand Ayatollah Khamenei: From the evening before Eid Al-Fitr can pay Zakat Al-Fitrah or put aside, and according to Wajib precaution; the responsible person (Mokallaf) must pay Zakat Al-Fitrah before Eid Salaat/Salaah, but if does not pray Eid Salaat can delay paying Zakat Al-Fitrah till before noon. And if can find a poor person, putting aside Zakat Al-Fitrah is not enough; but if cannot find a poor person, put aside Zakat Al-Fitrah and pay when the poor person is found. And if it is not put aside, according to Wajib precaution, the obligation is not removed, and must pay it with the intention of getting close to God (Qurbah); and without the intention of act (Ada) and Qadha.