Among the Arabs, agnomen is used for men and women for two reasons:
Because of possessing some perfection. For example, a person who is very obedient to Allah is named as“Abu-Abdullah” ; a person with extreme virtues and superiority as“Abu’l-Fazl” and a pious and righteous one as“Aba-Saleh” .
Because of his/her son’s name. In hope that he/she would possess a son in the future who would be named so. The agnomen of“Abu-Fazl” is given to him at the time of his birth or thereafter. The agnomen of“Umma-Fazl” is given to a woman in a similar position.
“Abu-Saleh” is one of the agnomens of our affectionate Imam and is more popular among the Arabs. While calling upon Imam and imploring help from him, they use this name. Muhaddis Nouri writes:
Ahmad-ibn-Muhammad-ibn-Khaled Barqi narrates in his book“Mahasin” from Abu-Baseer that Imam Sadeq (a.s.) said: “Whenever you lose your way, call out:
يا صالح! يا ابا صالح! ارشدنا الي الطريق! رحمكم الله
The word آدركني (= help me) is uttered by the one seeking and imploring for help. Therefore, the name“Aba-Saleh” used for Imam Mahdi (a.t.f.s.) takes its roots from traditions.