Sahih Bukhari Volume 4, Book 52, Hadith Number 208.
Narated By Anas : On the day (of the battle) of the Trench, the Ansar were saying, “We are those who have sworn allegiance to Muhammad for Jihaid (for ever) as long as we live.” The Prophet replied to them, “O Allah! There is no life except the life of the Hereafter. So honor the Ansar and emigrants with your generosity.”
And Narrated Mujashi: My brother and I came to the Prophet and I requested him to take the pledge of allegiance from us for migration. He said, “Migration has passed away with its people.” I asked, “For what will you take the pledge of allegiance from us then?” He said, “I will take (the pledge) for Islam and Jihad.”