Musnad Ahmad 27:105

Sufyan narrated to us, from al-Zuhri, from Salim, from his father, from the Prophet, peace and blessings of Allah be upon him, who said: "Whoever sells a slave who has wealth, his wealth belongs to the seller, unless the buyer stipulates [otherwise]. And whoever sells a date palm tree that has been pollinated, the fruit belongs to the seller, unless the buyer stipulates [otherwise]."