Volume 9, Book 89, Number 315:
Narrated Salama:
We gave the oath of allegiance to the Prophet under the tree. He said to me, “O Salama! Will you
not give the oath of allegiance?” I replied, “O Allah’s Apostle! I have already given the oath of allegi –
ance for the first time.” He said, (Give it again) for the second time.