Sahih Muslim Book 20, Hadith Number 4594.

Chapter : No migration after the conquest of Mecca but allegiance could be sworn (to a rightful leader) on serving the cause of Islam, on fighting in the way of Allah and on following the path of virtue.

It has been reported on the authority of Mujashi’ b. Mas’ud as-Sulami who said: I came to the Holy Prophet (may peace be upon him) to offer him my pledge of migration. He said: The period of migration has expired (and those who were to get the reward for this great act of devotion have got it). You may now give your pledge to serve the cause of Islam, to strive in the way of Allah and to follow the path of virtue.