Who was muhammad's father in law?

Prophet Muhammad had four daughters with his wife Khadija. The eldest Zainab was married to Abu al-Aas ibn al-Rabee, second daughter was Ruqqayah who was married to third Islamic Caliph Uthman Ibn Affan, Third daughter was Umm-e-Kulthum who married Uthman Ibn Affan after Ruqqayah's death. The youngest was Fatima who was married to prophet's cousin and fourth Islamic Caliph Ali ibn Abi Talib.