Riyad as-Salihin, Book 19, Hadith 1858 (In-Book) ⓘ
'Aishah (May Allah be pleased with her) said: The Prophet said, "If a person dies without observing Saum (fasts), his Wali should make it up on his behalf."[Al-Bukhari and Muslim].
وعنها رضي الله عنها عن النبي صلى الله عليه وسلم قال: "من مات وعليه صوم، صام عنه وليه" ((متفق عليه)).