Sahih Bukhari Volume 6, Book 60, Hadith Number 138.

Narrated By ‘Aisha : That her father (Abu Bakr) never broke his oath till Allah revealed the order of the legal expiation for oath. Abu Bakr said, “If I ever take an oath (to do something) and later find that to do something else is better, then I accept Allah’s permission and do that which is better, (and do the legal expiation for my oath)”.