'Aishah (May Allah be pleased with her) said:
The Prophet (ﷺ) said, "If a person dies without observing Saum (fasts), his Wali should make it up on his behalf."[Al-Bukhari and Muslim]. (RU)
App reference (RU): Book 19, Hadith 51 (RU)
Arabic/English book reference (RU): Book 19, Hadith 1858 (RU)