Is the gift of a non-existent item, such as the future yield of a tree or the offspring of a female slave, valid?

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The gift of a non-existent item, such as the future fruit of a tree or the expected offspring of a female slave, is invalid. This is because the contract of gift (*Hiba*) is a contract for the transfer of ownership during life, and therefore it is invalid for such future contingencies, analogous to the ruling on sale (*Bay'*) in this regard.