Oaths and Vows

Bukhari :: Book 8 :: Volume 78 :: Hadith 618

Narrated 'Aisha:

Abu Bakr As-Siddiq had never broken his oaths till Allah revealed the expiation for the oaths. Then he said, "If I take an oath to do something and later on I find something else better than the first one, then I do what is better and make expiation for my oath."