It was narrated from Jabir bin 'Abdullsh that :
a woman came to the Messenger of Allah (ﷺ) and said: "My mother has died, and she had made a vow to fast, but she died before she could fulfill it. The Messenger of Allah (ﷺ) said: 'Let her guardian fast on her behalf ." (IT)
English reference (IT): Vol. 3, Book 11, Hadith 2133 (IT)
Arabic reference (IT): Book 11, Hadith 2215 (IT)