Nafi' narrates from Ibn Umar (may Allah be pleased with them both) that the verse "Indeed, he has succeeded who purifies himself" [Surah al-A'la: 14-15] was revealed concerning sadaqat al-fitr.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7667
Kathir bin Abdullah al-Muzani narrates from his father, and he from his grandfather (may Allah be pleased with him), that the Messenger of Allah (peace and blessings be upon him) was asked about this verse: "Indeed, he has succeeded who purifies himself, and remembers the name of his Lord and prays" [Surah al-A'la: 14-15], and he (peace and blessings be upon him) said: "It refers to sadaqat al-fitr."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7668
A shaykh of Banu Sa'd narrates from Abu al-Aliyah (may Allah have mercy on him) that he said concerning "Indeed, he has succeeded who purifies himself" [Surah al-A'la: 14]: Sadaqat al-fitr is to be given, and then the Eid prayer is to be offered (Eid al-Fitr).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7669