Her husband was Sayyidina Hassan ibn Hassan ibn ‘Ali ibn Abi Talib radiya Llahu ‘anhum, commonly known as Hassan al Muthanna. His marriage to Sayyidah Fatimah bint Hussain rahimaha Llah is the first union between the houses of Hassan and Hussain radiya Llahu ‘anhuma. The ancestry of both husband and wife being Fatimi, Hashimi and ‘Alawi.
The ancestry of Fatimah bint Hussain rahimaha Llah is what prompted Sayyidina Miswar ibn Makhramah radiya Llahu ‘anhu to turn down the proposal of Hassan al Muthanna when he asked for his daughter’s hand in marriage. Al Hakim has reported with his chain of narration:
Hassan ibn Hassan wrote to Miswar asking for his daughter’s hand in marriage. Miswar asked him to meet him that evening which he did. Miswar said, “There is no association, lineage, or marital union more beloved to me than your lineage and having you as a son-in-law. However, I have heard the Prophet salla Llahu ‘alayhi wa sallam say, ‘Fatimah is a piece of me, what pleases her pleases me, and what upsets her upsets me. All relations will be severed on the day of Qiyamah except relationships to me.’ And you have in your wedlock her [grand] daughter; if I were to marry my daughter to you it would anger her.” Thus he excused himself.
This is the honourable man in whose wedlock she remained, from whom she received love and respect. A great proof of this is the grief she voiced in poetic verse on his demise:
لقد عظمت تلك الرزايا و جلت
وكانوا رجاء ثم أمسوا رزية
They were hopeful (in this life), and now they have been stricken with disaster.
How great and heinous are those disasters.
 Mustadrak al Hakim, # 4747. He deemed it sahih upon the conditions of al Bukhari and Muslim, and al Dhahabi concurred. The narration reported by Ibn ‘Asakir with his chain from Jafar ibn Muhammad from his father states, “Hassan ibn Hassan asked Miswar for the hand of his daughter in marriage, and in his wedlock at the time was Fatimah bint Hussain. So he replied, ‘O son of the Messenger salla Llahu ‘alayhi wa sallam, if you had asked for her hand in marriage even if it be for the Mahr (dowry) of one shoelace I would of certainly married her to you. However, I have heard the Messenger salla Llahu ‘alayhi wa sallam say “Fatimah is a piece of me, what pleases her pleases me, and what upsets her upsets me.” I know if she were alive and I had to marry my daughter to you while you are married to her daughter, it would have definitely upset her. I do not wish to be one who thus upsets the Messenger salla Llahu ‘alayhi wa sallam.’” Tarikh Dimashq, 74/17.
 Tarikh Dimashq, 74/16.