Sunan Ibn Majah, Chapter: The Chapters on Etiquette

"Abu Bakr went out to trade in Busra, one year before the Prophet (saw) died, and with him were Nu'aiman and Suwaibit the sons of Harmalah, who had been present at Badr. Nu'aiman was in charge of the provisions, and Suwaibit was a man who joked a lot. He said to Nu'aiman: 'Feed me'. He said: 'Not until Abu Bakr comes'. He said: 'Then I will have to annoy you'. Then they passed by some people, and Suwaibit said to them: 'Will you buy a slave from me?' They said: 'Yes'. He said 'He is a slave who talks a lot and he will tell you, "I am a free man". If you are going to let him go when he says that to you, do not bother buying him.' They said: 'We will buy him from you.' So they bought him from him in return for ten young she-camels, then they brought him and tied a turban or a rope around his neck. Nu'aiman said: 'This man is making fun of you. I am a free man, not a slave.' They said: 'He has already told us about you; and they took him off.' Then Abu Bakr came and he (Suwaibit) told him about that. So he followed those people and returned their camels to them, and took Nu'aiman back. When they came to the Prophet (saw) they told him what had happened, and the Prophet (saw) and his companions laughed about it for a year."