Musnad Ahmad 386:2

Abdullah ibn Ahmad said: Shayban ibn Abi Shaybah Abu Muhammad narrated to us, he said: Jarir—meaning Ibn Hazim—narrated to us, from Abu Ishaq al-Hamdani, who said: Dhu al-Jawshan came to the Prophet, peace and blessings of Allah be upon him, and gifted him a horse, and he was a polytheist on that day. The Messenger of Allah, peace and blessings of Allah be upon him, refused to accept it. Then he said: "If you wish, you may sell it to me, or would you like to sell it to me for the choice of the armor of Badr?" Then the Prophet, peace and blessings of Allah be upon him, said to him: "Would you like to be the first to enter into this matter?" He said: "No." The Prophet, peace and blessings of Allah be upon him, said to him: "What prevents you from that?" He said: "I saw your people have called you a liar, expelled you, and fought you. So look at what you do; if you prevail over them, I will believe in you and follow you, and if they prevail over you, I will not follow you." The Messenger of Allah, peace and blessings of Allah be upon him, said to him: "O Dhu al-Jawshan, perhaps if you remain..." and he mentioned the rest of the hadith similar to it.