Yahya related to me from Malik from Abd ar-Rahman ibn al-Qasimthat his father used to say, "If someone has to make up for days notfasted in Ramadan and does not do them before the next Ramadan comesalthough he is strong enough to do so, he should feed a poor man witha mudd of wheat for every day that he has missed, and he has to fastthe days he owes as well."Yahya related to me from Malikthat he had heard the same thing from Said ibn Jubayr.
USC-MSA web (English) reference: Book 18, Hadith 53
Arabic reference: Book 18, Hadith 686