Musnad Ahmad 189:3

Hassan ibn Musa narrated to us, he said: Shayban narrated to us, from Yahya ibn Abi Kathir, from Yahya ibn Ishaq, that he informed him from Mujashi ibn Mas'ud al-Bahzi, that he came to the Messenger of Allah, peace and blessings of Allah be upon him, with his brother's son to pledge allegiance to him for migration. The Messenger of Allah, peace and blessings of Allah be upon him, said to him: "No, rather he shall pledge allegiance for Islam, for there is no migration after the Conquest." He said: "And he shall be among those who follow in goodness."