Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) says that the Messenger of Allah (peace and blessings be upon him) ordered: "Sadaqat al-Fitr should be paid before the people go out to the Eid prayer ground."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7737
Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) says that the Messenger of Allah (peace and blessings be upon him) "ordered the payment of Sadaqat al-Fitr, that it be paid before the people go out to the Eid prayer ground," and Abdullah (may Allah be pleased with him) used to pay it one or two days before that.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7738
Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) says that the Messenger of Allah (peace and blessings be upon him) ordered us "to give Sadaqat al-Fitr on behalf of every young and old, free and slave: one sa' of dates or barley." He says: Raisins and cheese (aqit) were also brought to them, and they would accept it from them. And we were ordered "to give it before going out to the prayer." The Messenger of Allah (peace and blessings be upon him) ordered them to distribute it among them, and he would say: "Free them from the need to go around (begging) on this day."
This Abu Ma'shar is Najih al-Sindi al-Madani; others are more reliable than him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7739
Ja'far bin Burqan says: The letter of Umar bin Abd al-Aziz (may Allah have mercy on him) came to us, saying: Pay Sadaqat al-Fitr before the Eid prayer. "He has certainly succeeded who purifies himself, and mentions the name of his Lord and prays" [Surah al-A'la: 14-15]. And say as your father said: "Our Lord, we have wronged ourselves, and if You do not forgive us and have mercy upon us, we will surely be among the losers" [Surah al-A'raf: 23]. And say as Nuh (peace be upon him) said: "And unless You forgive me and have mercy upon me, I will be among the losers" [Surah Hud: 47]. And say as Ibrahim (peace be upon him) said: "And it is He who, I hope, will forgive me my sin on the Day of Recompense" [Surah al-Shu'ara: 82]. And say as Musa (peace be upon him) said: "My Lord, indeed I have wronged myself, so forgive me; and He forgave him. Indeed, He is the Forgiving, the Merciful" [Surah al-Qasas: 16]. And say as Yunus (peace be upon him) said: "There is no deity except You; exalted are You. Indeed, I have been of the wrongdoers" [Surah al-Anbiya: 87]. I think he also wrote that whoever has nothing to give as Sadaqat al-Fitr should fast after Eid. And Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7740