Musannaf Ibn Abi Shayba 7:157

Abu Bakr narrated to us, he said: Abu Bakr ibn Ayyash narrated to us, from Abd al-Aziz ibn Rufay, from Tamim ibn Tarfah, from Adi ibn Hatim, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever swears an oath, then sees something else that is better than it, let him abandon his oath and perform that which is better, and let him offer expiation for his oath."