Musannaf Ibn Abi Shayba 13:3150

Abu Bakr narrated to us, he said: Abd al-A’la narrated to us, from Ma’mar, from al-Zuhri, regarding a man who sold a slave of his for sheep, and the sheep increased [in number/value], then he found a defect in the slave that had been concealed from him. He said: He returns him, and he has the choice regarding his sheep: either he takes them [back] as they are, or he gives them to him as they are, just as he took them.