‘Uqbah ibn ‘Āmir (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "The conditions that are the worthiest of being fulfilled are those which make sexual intercourse lawful for you."
شرح الحديث :
Each spouse has his/her own purposes in getting married, thus the spouse may stipulate conditions (to serve these purposes), which become binding upon the other, apart from the conditions that are essential for the validity of marriage. Since it is by virtue of these conditions that enjoyment of sexual intercourse becomes lawful, they have great sanctity, and the Islamic law urged fulfilling them.