Ata' narrates from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) concerning this saying of Allah Almighty: "And upon those who are burdened with it (yutawwaqunahu)" [Surah al-Baqarah: 184], that is, they undertake it with hardship and are not able to do it; "the feeding of a poor person. But whoever volunteers good" [Surah al-Baqarah: 184], and so feeds another poor person, "it is better for him" [Surah al-Baqarah: 184]. This is not abrogated. Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: "No concession has been given in this except to the very old man who is not able to fast, and to the sick person who knows that he will not be cured."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8316