Imam Sadiq (A.S.) said: He (Imam Husayn) sees those, who come to his shrine and he knows them by their names, their father's names and their ranks in the eyes of Allah, The Mighty, The Glorious, better than you know your own children! Wasaail al Shiah vol 14, pg. 411.
Imam Ali ibne Musa ar-Reza (a.s.) said: Four thousand Angels descended from the heavens to aid Imam Hussain (a.s.), but when they reached there they saw that he had already been martyred. Thus, now they all remain near his blessed grave with disheveled hair covered with dust until the rising of the Qaem (Imam al Mahdi). Then they will all aid him and their slogan will be: Vengeance for the blood of Husain. Ref: Nafasul Mahmum, Section-1, Tradition No.1