Abu al-Sha'tha' (may Allah have mercy on him) said: (The condition to be fulfilled) is that by which her private part was made lawful.
Al-Zuhri and others said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever stipulates a condition that is not in the Book of Allah, it counts for nothing, even if it be a hundred conditions."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14440