What is the difference between waiver (al-tanazul) and gift (al-hibah) in Islamic Sharia, and is it a condition that there be no compensation in either of them? What is the ruling on exchanging gold with a waiver of the difference, and is it considered a legitimate waiver for an heir to waive his share in an apartment to his brother in exchange for the latter residing in it as a tenant under the old law?

A gift (hiba) can be made conditional upon a return ( عوض), in which case it is called a gift of recompense (hibat al-thawab). If it is without a return, it is the transfer of ownership of a valuable asset without compensation. A waiver (تنازل) can be with or without a return.

If an exchange occurs between gold and gold, they must be equal, and it is not permissible for one to be heavier than the other, based on the Prophet's (peace be upon him) saying: "Do not sell gold for gold unless it is like for like, and do not prefer one over the other."

The Malikis have made an exception in the case of exchange, allowing each piece to exceed the one taken in exchange by one-sixth, provided that the lesser piece is not of superior quality, finer minting, or better craftsmanship.

As for one heir saying to another: "I waive my claim to your apartment, which you inhabit by virtue of your inheritance, on the condition that you remain in it as an old tenant," this is a contract that involves gharar (uncertainty/ambiguity), establishes falsehood, and contains جهالة (ignorance of essential terms), and therefore it is not permissible.