Is it permissible for a man to remain with his wife who has not borne him children and has reached menopause, knowing that he has had children with another woman and cannot combine two wives?

It is permissible for a husband to keep his wife who does not bear children with him, as this does not fall under the forbidden celibacy (tabattul). However, it is desirable for him to marry a fertile, loving woman to join her with his first wife and treat them both justly, due to the hadith: "Marry the fertile, loving woman, for I will boast of your multitude." If it is not possible to combine them, then the advice is to divorce the first wife and marry a fertile one.