Imam Ja’far as Sadiq (a.s.) said, that when Imam Husayn (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.”
Reference : Nafasul Mahmoom – Shaikh abbas Qummi (r.a.)