Sahih Bukhari: Hadith 1888

A man came to the Prophet (ﷺ) and said, "O Allah's Messenger (ﷺ)! My mother died and she ought to have fasted one month (for her missed Ramadan). Shall I fast on her behalf?" The Prophet (ﷺ) 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 (ﷺ) "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."