Sunan Ibn Majah Book 19, Hadith 1
the Messenger of Allah (ﷺ) sold a Mudabbar.
“I heard my father narrate from Abu Hurairah that the Prophet (ﷺ) said: 'Among those who came before you there was a man who bought some property and found therein a jar of gold. He said: “I bought land from you, but I did not buy the gold from you.” The man said: “Rather I sold you the land with whatever is in it.” They referred their case to (a third) man who said: “Do you have children?” One of them said: “I have a boy.” The other said: “I have a girl.” He said: “Marry the boy to the girl, and let them spend on themselves from it and give in charity.”
“A man among us promised freedom to a slave after his death, and he did not have any property other than him (this slave). So the Prophet (ﷺ) sold him, and Ibn (Nahham), a man from Banu 'Adi, bought him.”