A Bedouin seeking forgiveness through the Prophet (peace and blessings be upon him)

It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that a young man from among the sons of the Muhajirun came to the Messenger of Allah (peace and blessings be upon him) and said: O Messenger of Allah (peace and blessings be upon him), pray for forgiveness for me. The Messenger of Allah (peace and blessings be upon him) was occupied with something. He repeated his request three times, and when he saw that the Messenger of Allah (peace and blessings be upon him) was not seeking forgiveness for him, the young man said three times before the Messenger of Allah (peace and blessings be upon him): 'Allahumma-ghfir li, Allahumma-ghfir li, Allahumma-ghfir li, fa inna rasulaka lam yastaghfir li' (O Allah, forgive me; O Allah, forgive me; O Allah, forgive me, for Your Messenger has not sought forgiveness for me). When the young man left, Jibril (peace be upon him) came down to the Messenger of Allah (peace and blessings be upon him) and said: O Messenger of Allah (peace and blessings be upon him), why did you not seek forgiveness for this young man? Allah has already forgiven him. So go after him until you inform him that Allah has forgiven him, and tell him to seek forgiveness for you. So the Messenger of Allah (peace and blessings be upon him) went quickly after him until he caught up with him, and when he reached him he said: "O young man, Allah, the Mighty and Majestic, has forgiven you, so now seek forgiveness for me." The young man said: 'Allahumma astaghfiruka li-rasulika, Allahumma inni astaghfiruka li-rasulika wa nabiyyika kama ghafarta li, innaka wasi'ul-maghfirah, wa anta arhamur-rahimin' (O Allah, I seek Your forgiveness for Your Messenger; O Allah, I seek Your forgiveness for Your Messenger and Your Prophet just as You have forgiven me; indeed You are vast in forgiveness, and You are the Most Merciful of those who show mercy).

A similar hadith is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him).
This hadith is gharib (unusual) in both its chain and its text. All of its narrators are trustworthy (thiqah) except Muhammad bin Abi Muslim, who is unknown (majhul). And Allah knows best.