Riyad as-Salihin 1858
'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] .
وعنها رضي الله عنها عن النبي صلى الله عليه وسلم  قال‏:‏ ‏
"‏من مات وعليه صوم، صام عنه وليه‏"‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏