The marriage of Umar (may Allah be pleased with him) to Umm Kulthum (may Allah be pleased with her) and its reason

It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Looking at the face of Ali is worship."

It is narrated from Sayyiduna Ali bin al-Husayn that Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) asked Sayyiduna Ali (may Allah be pleased with him) for the hand of his daughter Umm Kulthum and said: "Marry her to me." Sayyiduna Ali (may Allah be pleased with him) said: "I have reserved her for my nephew Abdullah bin Ja'far." Sayyiduna Umar (may Allah be pleased with him) insisted, saying: "Marry her to me, for by Allah! There is no one among the people who hopes to gain from this match the virtue that I seek." So Sayyiduna Ali (may Allah be pleased with him) married her to Sayyiduna Umar (may Allah be pleased with him). Then Sayyiduna Umar (may Allah be pleased with him) came to the Muhajirun and said: "Will you not congratulate me?" They asked: O Commander of the Faithful! On what occasion? He said: "On my marriage to Umm Kulthum (may Allah be pleased with her), the daughter of Sayyiduna Ali (may Allah be pleased with him) and the granddaughter of the Messenger of Allah (peace and blessings be upon him), for I heard the Messenger of Allah (peace and blessings be upon him) say: 'Every lineage and tie by marriage (sabab) will be cut off on the Day of Resurrection except my lineage and my tie.' So I wished that there be a tie of lineage and marriage between me and the Messenger of Allah (peace and blessings be upon him)."
This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.

It is narrated from Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said to me: "It is a firm covenant that this Ummah will soon, after me, be disloyal to you. You will live upon my religion and be martyred upon my Sunnah. Whoever loves you has loved me, and whoever hates you has hated me. And indeed this (beard) will be dyed from this (the blood of the head)."
This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.

It is narrated from Sayyiduna Hudhayfah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "If you make Abu Bakr the ruler, he is detached from the world and seeks the Hereafter, though there is some frailty in his body. If you make Umar the ruler, he is strong and trustworthy, and in the matter of Allah he does not care about the blame of any blamer. And if you make Ali the ruler, he is himself rightly guided and guides others to the way; he will keep you firm upon the Straight Path."
This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.
[A brief account of the martyrdom of the Commander of the Faithful Ali bin Abi Talib (may Allah be pleased with him), with the most authentic chains of narration]