Is it valid for a sister to give her mother money as a gift, on the condition that the mother returns it if the sister needs it, and is it permissible for the mother to take this money if the sister's intention is to disinherit the other heirs?

A gift stipulated with an unknown consideration, according to the majority of scholars, is a void sale, and the gift becomes invalid. The donee must return the item to the donor. Its ruling is that of a void sale. The Hanbalis, however, are of the view that it is valid if a consideration is given that satisfies the donor.

Some jurists hold that it is a valid gift from beginning to end, and the condition of an unknown consideration is void. The gift is not invalidated by a void condition. So, if the mother fulfilled her aunt's condition until her death, the money belongs to her alone, excluding the rest of the heirs. This issue involves a difference of opinion, and only a ruling by a Sharia (definition) judge can resolve the dispute.

As for the intention to disinherit heirs, it is considered reprehensible by some and forbidden by others. If the gift occurred while the donor was in good health, it is enforceable according to most scholars, even if the intention was to disinherit heirs.