From Sahih Bukhari (Hadith 2379):
Narrated 'Abdullah (ra): I heard the Messenger of Allah (ﷺ) say, "If somebody buys date-palms after they have been pollinated, the fruits will belong to the seller unless the buyer stipulates the contrary. If somebody buys a slave having some property, the property will belong to the seller unless the buyer stipulate that it should belong to him
Reference: Bukhari 2379