Shaikh Mufeed has narrated through his chain of transmitters, that Imam Ja'far as Sadiq (a.s) said, that when Imam Husain (a.s) left Madina, a group of Angels, having distinct marks, met him on the way. They carried swords in their hands and had mounted the horses of Paradise. They came to Imam, saluted him and said, "O Allah's Proof (Hujjah) upon the creatures after your Grandfather, Father and Brother! Allah the Glorious had rendered help to your Grandfather through our medium in many of his battles, and has now sent us to assist you." Imam replied,
"The promised land is called Karbala, thus you may come to me there."
They said, "O Proof of Allah! You may command whatever you desire and we will comply to it and obey you. If you fear the enemies we shall defend you against them." Imam replied,
"They have no way upon me and they will not be able to hurt me until I reach my (destined) mausoleum."
The army of genie in defense of Imam Husain (a.s)
Numerous groups of Muslim genie came to Imam Husain (a.s) and said, "O our Master! We are your adherents and helpers thus we shall fulfil your command, whatever it be. If you desire we will hault here and slay all your enemies." Imam replied,
"May Allah reward you with goodness! Haven't you read the Qur'an which was revealed to my Grandfather, wherein is stated:
"Wherever you be, death will overtake you, even if you be in towers (strong and) lofty."[1] and it is stated, "Those for whom slaughter was ordained would certainly have gone forth to the places where they (now) lie (slain)."[2]
Then if I remain in this place, how would this unfortunate nation be tested and tried? And who will lay in my grave in Karbala. (On the day) When Allah the Glorious spread the earth, He chose that land for me. And has made it a place of refuge for my followers (Shi'ah) so that they might find
[1] Surah an Nisa: 78.
[2] Surah Ale Imran: 154
peace thereunder in this world as well as the hereafter. Come to me on Saturday, for I shall be martyred in the end of the week on the tenth. No one from among my family, friends, brothers and relatives will remain alive after my death, my head will then be taken to Yazeed."
The genie said, "O friend of Allah! And O the son of the friend of Allah! If the obedience of your orders would not have been obligatory on us and killing would not have been unlawful, we would surely have killed all your enemies before they reach you." Imam replied,
"By Allah! We are competent enough to kill them than you. But the intention is that one should be killed with (presenting valid) proofs and reasons, and should be guided with proofs and reasons."
In other words, the Imam did not wish that they be destroyed before submitting his proofs unto them. (Here ends that which has been quoted in the book of Mohammad bin Abi Talib)
source : http://www.maaref-foundation.com