Narrated Ibn Abbas (RA):
Sa'd bin Ubada asked Allah's Messenger (ﷺ) for a ruling regarding a vow taken by his mother who had died before fulfilling it, and he said, "Fulfill it on her behalf." [Agreed upon]. (PT)
Reference (PT): Bulugh al-Maram 1391 (PT)
In-book reference (PT): Book 13, Hadith 18 (PT)
English translation (PT): Book 13, Hadith 1391 (PT)