Musnad Ahmad 100:3

'Abd al-Rahman ibn Mahdi narrated to us, from Sufyan, from Ibrahim—meaning Ibn Muhajir—from Mujahid, from the leader of al-Sa'ib, from al-Sa'ib, that he said to the Prophet (peace and blessings of Allah be upon him): "You were my partner, and you were the best of partners. You would neither deceive nor dispute."