Qur'an 4:129You will not be able to treat your wives with absolute justice not even when you keenly desire to do so. (It suffices in order to follow the Law of Allah that) you incline not wholly to one, leaving the other in suspense. If you act rightly and remain God-fearing, surely Allah is All-Forgiving, All-Compassionate.
This means that it is not possible for a man to accord complete equality of treatment to two or more wives under all circumstances and in all respects