And Hasan al-Basri, may Allah have mercy on him, said that if thirty people fast for one day on his behalf (in place of the thirty days of Ramadan), it is permissible.
Narrated `Aisha: Allah's Apostle said, "Whoever died and he ought to have fasted (the missed days of Ramadan) then his guardians must fast on his behalf."
Hadith Referenceصحيح البخاري / كتاب الصوم / 1952
Hadith Gradingمحدثین:أحاديث صحيح البخاريّ كلّها صحيحة
Narrated Ibn `Abbas: A man came to the Prophet and said, "O Allah's Apostle! My mother died and she ought to have fasted one month (for her missed Ramadan). Shall I fast on her behalf?" The Prophet replied in the affirmative and said, "Allah's debts have more right to be paid." In another narration a woman is reported to have said, "My sister died..." Narrated Ibn `Abbas: A woman said to the Prophet "My mother died and she had vowed to fast but she didn't fast." In another narration Ibn `Abbas is reported to have said, "A woman said to the Prophet, "My mother died while she ought to have fasted for fifteen days."
Hadith Referenceصحيح البخاري / كتاب الصوم / 1953
Hadith Gradingمحدثین:أحاديث صحيح البخاريّ كلّها صحيحة