Ali bin Husayn (may Allah have mercy on him) said: When Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) married Sayyidah Umm Kulthum bint Ali (may Allah be pleased with her), he came to a gathering in the mosque of the Messenger of Allah (peace and blessings be upon him), between the grave and the pulpit, which was for the Muhajirun; no one else used to sit in it. They prayed for blessing for him. He (may Allah be pleased with him) said: "I married her only because I heard the Prophet (peace and blessings be upon him) saying: 'Every tie of kinship and lineage will be cut off on the Day of Resurrection, except my tie and my lineage.'"
This is a good (hasan) mursal report, and it has also been narrated through other routes, both connected (mawsul) and mursal.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13393