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