Shaikh Saduq (May Allah sanctify his grave) quotes Imam Ja’far as Sadiq (a.s.) as saying that when Imam Husayn (a.s.) was born, Allah commanded Jibra’eel to descend upon the earth with a thousand Angels and congratulate the Prophet on His behalf and himself. Jibra’eel descended and on the way he passed by an island where an Angel named Fitrus, who was a bearer of the empyrean, lay there banished.
Allah had once assigned a job to Fitrus who delayed it due to laziness; hence Allah took away his wings and expelled him to the island. Fitrus worshipped Allah there for seven hundred years until the time Imam Husayn (a.s.) was born. When Fitrus saw Jibra’eel he inquired of him as to where was he going. Jibra’eel answered that, “Allah, the Exalted, has bestowed His Blessings (Imam Husayn) upon Muhammad (S), thus Allah has commanded me to go and congratulate him on His behalf and myself.” Fitrus said,
“Then O Jibra’eel! Take me too along with you to the presence of the Prophet, perhaps he might pray for me.”
Jibra’eel lifted him up and brought him to the Holy Prophet (S). When he reached there he offered condolence to him on behalf of Allah and himself, then he presented the matter of Fitrus. The Prophet commanded Fitrus to touch himself with the body of Imam Husayn (a.s) and arise. Fitrus did so and ascended upwards saying,
“O Prophet of Allah! This son of yours will be mercilessly killed by your nation. Therefore it is incumbent upon me in exchange of this favor that I recompense. Hence there is no person who visits his grave except that I receive him, and there is no Muslim who offers salutations to him or who prays for him except that I take it to his presence and carry his message.”
Saying this Fitrus flew away. In another narrative it is related that Fitrus flew away saying,
“Who is similar to me? For I am a freed one of Husayn (s.a.s), the son of Ali (a.s.) and Fatima (a.s.), whose Grandfather is Ahmad (S).”
Reference : Nafasul Mahmoom – Shaikh abbas Qummi (r.a.)