It has been reported on the authority of Mujashi' b. Mas'ud who said

I brought my brother Abu Ma'bad to the Messenger of Allah (may peace he upon him) after the conquest of Mecca and said: Messenger of Allah, allow him to swear his pledge of migration at your hand. He said: The period of migration is over with those who had to do it (and now nobody can get this meritorious distinctions) I said: For what actions will you allow him to bind himself in oath? He said: (He can do so) for serving the cause of Islam, for fighting in the way of Allah and for fighting in the cause of virtue. Abd Uthman said: I met Abd Ma'bad and told him what I had heard from Mujashi'. He said: He has told the truth.