ibn-hajar in 'sawa'eq' (page 98) has narrated from ibn-maaja as such:
'a group of people will rise from the east and they will make preparations for Mahdi's rule.'
the author of 'eqdud-durar' (in chapter five) has narrated the same tradition from ibn-maaja and baihaqi.
the author of 'eqdud-durar' (in chapter five) has narrated from abu na'eem (book of sefat-ul-Mahdi) who has narrated from sauban that the messenger of Allah (s.a.w.a.) said: when you see black flags coming from the direction of east, hasten towards them even if you have to crawl over ice because Mahdi who is Allah's representative will be amongst them.
narrator says: hakim abu abdullah in 'mustadrak', and imam abu omar in 'sunan' and hafiz na'eem-ibn-hemad in 'fatan' have narrated the contents of this tradition. perhaps the saying: 'Mahdi who is Allah's representative will be amongst them means that the rudiments of Mahdi's rule would be in their hands just as the same was mentioned in the tradition of abdullah-ibn-harith.
in the same chapter of the afore-said book, its author narrates from sa'eed-ibn-musaiyeb that the messenger of Allah (s.a.w.a.) said: a man from bani abbass will rise from the east and will remain on the land until Allah wishes. thereafter a group with small black flags will emerge and they will battle with the people from the progeny of abu sufyan and his followers and will prepare the ground for Mahdi's obedience and submission.
author says: some of the traditions which speak about the appearance of black flags from the east refers to the invitation of abbassid and uprising of abu muslim khurasani. yet, some other traditions signal out the uprising of a group from the east who would invite (the people) towards Mahdi (a.s.) and the tradition of sa'eed-ibn-musaiyeb which was mentioned before, refers to this account. the possibility which we mentioned previously about the traditions (in this regard) being fabricated refers to the first type of interpretation. so do not be heedless about them.
the author of 'yanabi-ul-muwadda' (page 448) narrate from the book 'fara'ed-us-semtain' which narrates from hafiz abu naeem that imam muhammad baqir (a.s.) said: 'Allah has set fear in the hearts of our friends and followers. when our 'qa'em' who is Mahdi will emerge, one person from our followers will be more courageous than a fierce lion and more sharper than the point of a spear.
author says: undoubtedly, a group which loses its leader also loses its will-power and aim and rather its very progress as against a group possessing a leader with an upright will-power, earnest aim and firm power. this is because such a state eventually leaves an impression on the conduct and morale of that group. it seems that the afore-mentioned tradition too refers to this very matter and the reason why god has set fear in their hearts is to protect them.