Musnad Ahmad 627:29

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, he said: I heard 'Abd al-'Aziz ibn Rufay' narrating, he said: I heard Tamim ibn Tarafah narrating from 'Adi ibn Hatim, he said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Whoever swears an oath, then sees another [course of action] that is better than it, let him come to that which is better, and let him leave his oath."