Musnad Ahmad 1153:393

Harun narrated to us, Ibn Wahb narrated to us, he said: Haywah said: Salim informed me that he presented this hadith to Yazid, and he recognized it, that Urwah ibn al-Zubayr said: Aisha informed me that the Messenger of Allah, peace and blessings of Allah be upon him, said: "Whichever deceased person dies while having [unfulfilled] fasting [obligations] upon him, then his guardian should fast on his behalf."