Musannaf Ibn Abi Shayba 13:473

Abu Bakr narrated to us, he said: 'Abdah bin Sulayman narrated to us, from Muhammad bin Ishaq, from Yazid bin Abdullah bin Qusayt, who said: Ali sold a camel for two camels. The one who bought it from him said to him: "Hand over my camel to me until I bring you your two camels." Ali said: "You shall not part with the halter of my camel until you bring my two camels."