On Breaking An Obligatory Fast on Purpose
by The Albaani Site
Questioner: Does [extra] optional fasting help someone who has broken his [obligatory] fast intentionally, since there is no proof that breaking an obligatory fast can [actually] be made up for?
Al-Albaani: There is no doubt that it will help him, just like someone who missed lots of [other] obligatory duties, compensating for what he missed by performing supererogatory prayers will help him.
There is no way for a person who breaks his [obligatory] fast on purpose to make up for it, and he is extremely sinful [for doing that] until he truly repents to Allaah عزو جل. He should [try and] offset the good deeds that he has missed out on because of breaking the fast on purpose by performing lots of supererogatory prayers until he make amends for some of what he has missed.
Al-Hudaa wan-Noor, 19.