Musannaf Ibn Abi Shayba 7:161

'Abd al-Rahim narrated to us, from Yahya ibn Sa'id, from al-Qasim, who said: Abu Bakr, may Allah be pleased with him, used to not consider himself to have broken an oath if he swore one, until this verse was revealed: "Allah will not impose blame upon you for what is unintentional in your oaths." So, if he swore an oath and then saw something else that was better than it, he would do that which was better and offer expiation for his oath.