Ata' said: I heard Ibn Abbas (may Allah be pleased with them both) recite: "And upon those who are burdened with it (yutawwaqunahu) is a ransom: the feeding of a poor person" [Surah al-Baqarah: 184]. Then Ibn Abbas (may Allah be pleased with them both) said: This is not abrogated; rather, it is for the very old man and the very old woman who are unable to fast, so they should feed a poor person in place of each day.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8315