‏الأيمان : Hadeeth No:4054 Abu Huraira reported Allaah's Messenger (sallAllaahu alayhi wa sallam) as saying: He who took an oath and (later on) found another thing better than that, he should do that which is better, and expiate for the vow (broken by him)....

‏الزكاة : Hadeeth No:2193 This hadith has been narrated by Shu'ba with the same chain of transmitters....