Is it permissible for a husband to question his wife about how she spent her dowry after she has spent it all on her preparations, especially since he had hoped she would return part of it to him?

The Mahr (dower) is an exclusive right of the woman; she disposes of it as she wishes. The husband has no right to demand anything from his wife from it, unless she willingly and graciously offers it to him, as Allah the Almighty says: "And give women their Mahr as a free gift. But if they, of their own good pleasure, remit any part of it to you, take it, and enjoy it with good cheer." The husband has no right to dispute with her concerning it or question her about it with disapproval, as a mature woman has the right to dispose of her wealth without her husband's permission.