Condition before Accepting Islam: Before accepting Islam, Hazrat Abu Zar (radhiyallahu ‘anhu) was a highway-robber. He was so brave and courageous that he would, without any assistance, single handedly rob travelers. He would waylay the caravans that would stop for water in the early morning. He would attack them from horseback or on foot with great speed and talent.

(Siyar A‘laam min Nubalaa 3/373)

Hazrat Abu Zar (radhiyallahu ‘anhu) believed in Tauheed (the Oneness of Allah Ta‘ala) prior to the advent of Islam. He had begun worshiping Allah Ta‘ala three years before embracing Islam at the hands of Nabi (sallallahu ‘alaihi wasallam).

(Usdul Ghaabah 1/343)