Musnad Ahmad 189:5

Ahmad ibn Abd al-Malik ibn Waqid narrated to us, he said: Zuhayr narrated to us, he said: Asim al-Ahwal narrated to us, from Abu Uthman al-Nahdi, from Mujashi’, he said: I came with my brother, Ma’bad, to the Prophet, peace and blessings of Allah be upon him, after the Conquest. I said: "O Messenger of Allah, I have brought my brother to you so that you may take his pledge of allegiance for migration." He said: "The people of migration have gone with what was in it." I said: "Upon what thing will you take his pledge of allegiance?" He said: "Upon Islam, faith, and Jihad." He said: So I met Ma’bad afterward—and he was the elder of the two—and I asked him, and he said: "Mujashi’ spoke the truth."