Umar at Fatimah's house refers to the controversial event where Umar came to the house of Fatimah, the daughter of the Islamic prophet Muhammad, in order to get the allegiance of Ali and his followers or burn her house down. This event, according to Shias, is said to be the cause of Fatimah's miscarriage of Muhsin ibn Ali and eventual death.
According to the sources, following the death of Muhammad, Abu Bakr and Umar attempted to gain the shura (consensus) of the community that Abu Bakr should become the caliph (leader) over the Islamic ummah (community). According to Shi'a sources, as Ali attended the funeral of Muhammad, Abu Bakr and Umar attained the consensus of the community. As Ali was burying Muhammad, he learned that Abu Bakr had attained communal consensus. Fatimah, Ali, and their supporters maintained that Ali should be the leader over the Islamic community because of Muhammad's statement at Ghadir Khumm.
After Abu Bakr became caliph, he sent for Ali to demand his allegiance. At the time, Ali and his supporters had gathered in Fatimah's house. There are multiple versions of what happened, ranging from Umar threatening to burn down the place if Ali refused to comply, to storming the house during which Fatimah miscarried Muhsin.
Tabari adds that Zubayr came out of the house with his sword drawn, but stumbled and was overpowered by Umar's men.Veccia Vaglieri says that it was Ali who came to Umar with his sword drawn and was subsequently disarmed, after which Fatima cried and threatened to uncover her hair so that Abu Bakr preferred to withdraw.
Muhammad ibn Jarir al-Tabari cites Abu Bakr on his deathbed saying that he wished he had never opened Fatima's house to anything, even though they had locked it as a gesture of defiance, implying that her house may have been broken into forced open.
According to Sunni books of Hadith and books of history written at the time however, this entire story did not occur. It states that Ali willingly gave oath of allegiance to Abu Bakr, though maintained a distance from him out of respect for Ali's wife Fatima, because of an argument Abu Bakr had with Fatima over her inheritance. When Fatima died 6 months later, Ali went to Abu Bakr to re-establish closer relations. It is further refuted considering that Umar married Ali and Fatima's daughter, Umm Kulthum, whom he married after Abu Bakr taking Khilafa, showing the good relations he had with Ali at the time.