The Ruling on Fasting on Behalf of the Deceased

Question:
Umm Hudhayfah asks and says: Is it permissible for a living person to fast for a deceased person, so that he fasts and intends the fast for the deceased? May Allah reward you with good.

Answer:
If it is a fast of a vow, yes. The Prophet (peace and blessings be upon him) said: Because the fast of a vow is a debt in the responsibility of the one who made the vow, so it is paid on his behalf. As for the fast of Ramadan, a fast that is obligatory by the original law of the Shari'ah, this is a matter of disagreement among the scholars: whether it is fasted on his behalf or not? And if someone fasts on his behalf as a precaution, that is good. Yes.