Musannaf Ibn Abi Shayba 13:2070

Abu Bakr narrated to us, he said: Ibn Abi Za’idah narrated to us, from Ash’ath, from Muhammad, who said: A man sold a sick camel to a man and stipulated [that he keep] its head, and he held onto it. Then the camel recovered, but he did not slaughter it. Shurayh said to him: "Give him its equivalent value (shirwah)." I mentioned that to ‘Amir, and he said: "Ali and Shurayh both judged by [the rule of] the equivalent value (shirwah)."