Sahih Bukhari

Narrated Salama:We gave the oath of allegiance to the Prophet (ﷺ) under the tree. He said to me, ""O Salama! Will you not give the oath of allegiance?"" I replied, ""O Allah's Messenger (ﷺ)! I have already given the oath of allegiance for the first time."" He said, (Give it again) for the second time