Ali weds Lady Ummol-Baneen

The world around the Holy Prophet witnessed and history has vouched the fact that the gap in the domestic life and the happiness of the Prophet, created by the demise of Lady Khadija doubtlessly proved as irreparable for no other woman fittingly filled it up to give the Apostle of God the happiness at home or the harmony in his domestic life, and it is only about the good Lady Omme Salema that the Holy Prophet said: Ante ala! Khair,' i.e., Thou art on goodness, which the good Lady proved true by not leaving the house of the Holy Prophet even after his departure from this world, and remaining as attached to his Ahlul.-Bait as she was during his lifetime. The same was the case with Ali the First Imam, the Vicegerent of God on earth, succeeding the Holy Prophet. After the martyrdom of the Holy Lady Fatema, there was none in the world to take her holy place in the house of Ali and the good Lady Ommol-Baneen served Ali after Holy Lads' Fatema as did Omme Salema to the holy Prophet after the demise of Lady Khadija.

 The alliance for a Holy Cause

The prophecy from the Holy Prophet about the impending Zibhe Azeem' or the Great Martyrdom of Husain, had gained so much currency and had become a matter of such a conviction and concern to the Ahlul-Bait that after the departure of Lady Fatema, 'A1i called his brother Aqeel who was known for his knowledge about the tribal genealogies and told him to find out a respectable lady of a noble family, known for its bravery, for him to wed for he wanted to have a brave son from her to be his own representative there at Karbala to serve Husain the son of the Holy Prophet and help him in the calamitous situation against his enemies and lay his life defending Husain on his own behalf, for Hasan and Husain were hailed as the sons of the Holy Prophet and each one was addressed as Ibne Rasoolullah' (son of the Holy Prophet).

Source - Husain The Saviour of Islam, by S.V. Mir Ahmad Ali.