Musannaf Ibn Abi Shayba 13:3162

Abu Bakr narrated to us, he said: Jarir narrated to us, from Mansur, from Ibrahim, who said: If a man buys a beast and finds a defect in its tooth, and he wishes to return it, then he must swear by Allah that it is only because of its tooth that he is returning it. And if it was a defect other than that, he does not have to swear.