If a man falls ill during Ramadan and then dies without having fasted, food is given in charity on his behalf and there is no obligation of make-up fasting upon him. But if he had a vow of fasting upon him, his guardian fulfills it on his behalf.
حدثنا محمد بن كثير أخبرنا سفيان عن أبي حصين عن سعيد بن جبير
إذا مرض الرجل في رمضان ثم مات ولم يصم أطعم عنه ولم يكن عليه قضاء وإن كان عليه نذر قضى عنه وليه
No references are available.
[Its chain is daif] Abdul-Razzaq narrated it in al-Musannaf, no. 7630, from Sufyan Thawri through this route, and I did not find an explicit statement of his hearing it.