Musannaf Ibn Abi Shayba 13:2260

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sufyan narrated to us, from ‘Abd al-‘Aziz ibn Rufay’, he said: I sold a slave girl to a man and I stipulated to him that I would sell her to myself. He said: So I sold her to myself. Then I disputed with him before Shurayh. He said: You have acknowledged the sale, so [produce] your evidence for the condition.