We have in our books that Lady Umm Kulthoum Bint Ameerul Mo'mineen was married to Aon son of Abdullah ibn Jafar Tayyar. There is fabricated still famous narration that she was married to Umar ibn al-Khattab. This narration was fabricated and the narrator of it is Zubair ibn Bakkar who was an open enemy of Ahlul Bayt (AS). Many books are available refuting this false story including إفحام الاعداء والخصوم بتكذيب زواج سيدتنا أم كلثوم by Allamah Sayyed Nasir Hussain of Lucknow.
Wassalam.