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."
— Sahih Bukhari, Volume 8, Book 78: Oaths and Vows, Hadith #618