Is it permissible for a man to buy a gold gift for one of his wives, but not the other, knowing that he is not remiss in the rights of the other wife, and is this considered a lack of justice between wives?

A man with more than one wife must deal justly with them in terms of maintenance, housing, and overnight stays. He is not permitted to favor one over another. The Prophet, peace and blessings be upon him, warned that whoever inclines to one of his wives over the other will come on the Day of Resurrection with one side of his body drooping. This is evidence of the obligation to be just between wives and the prohibition of a husband inclining to one of them in a way that diminishes the right of the other, except for the inclination of the heart, which a person does not control. The husband should not exclusively give one of his wives something he possesses without giving the other. If he gives something to one of them, he must give the other something similar or its value, unless the other wife permits it.