‘Abdullāh ibn ‘Umar (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "If someone sells pollinated date palms, their fruits will be for the seller, unless the buyer stipulates the contrary." In another narration: "And if someone buys a slave, his property is for the seller, unless the buyer stipulates the contrary."
He determined that pollination and its fruits belong to the seller, for he is the one who did the work that was required for this. However, if the buyer stipulates that the fruits shall be for him, though the palm trees have been pollinated, and the seller agrees, then they should abide by this condition. The same applies to a slave who is granted some property by his master. If his master sells him, the property shall go back to the seller, for it is not covered by the sales contract. However, if the buyer stipulates that he shall take all or part of the slave's property, this shall be part of the contract.