Allah's Messenger (ﷺ) said, "Whoever died and he ought to have fasted (the missed days of Ramadan) then his guardians must fast on his behalf."
Sahih al-Bukhari Book 30, Hadith 59
← Previous Hadith The Prophet (ﷺ) said, "Isn't it true that a woman does not pray and does not fast on menstruating? And that is the defect (a loss) in her religion."

Sahih al-Bukhari Book 30, Hadith 58 Next Hadith → 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."

Sahih al-Bukhari Book 30, Hadith 60