Is it permissible to give zakat to a destitute relative, and when he becomes well-off, he returns it, but the zakat-giver refuses to accept it?

If the relative benefiting from the Zakat is poor and not someone whose maintenance is obligatory upon the Zakat-giver, then the Zakat is permissible for him, and he should not return it, because he has taken ownership of it upon receiving it. After that, it is not permissible for the Zakat-giver to reclaim it.