The Adherence of Hazrat Abu Zar (radhiyallahu ‘anhu) to the Instruction of Rasulullah (sallallahu ‘alaihi wasallam):

When Hazrat Abu Zar (radhiyallahu ‘anhu) left Shaam and arrived in Madinah Munawwarah, Hazrat Uthmaan (radhiyallahu ‘anhu) said to him, “Why don’t you stay with me? The milk-giving she camels will come to you in the morning and evening.” Hazrat Abu Zar (radhiyallahu ‘anhu) declined this offer and replied, “I do not have any need for your wealth.” Hazrat Abu Zar (radhiyallahu ‘anhu) thereafter asked Hazrat Uthmaan (radhiyallahu ‘anhu) for permission to settle in Rabzah to which Hazrat Uthmaan (radhiyallahu ‘anhu) consented. When Hazrat Abu Zar (radhiyallahu ‘anhu) arrived in Rabzah, the salaah was commencing and the Imaam was an Abyssinian slave belonging to Hazrat Uthmaan (radhiyallahu ‘anhu). On seeing Hazrat Abu Zar (radhiyallahu ‘anhu), the slave moved back so that Hazrat Abu Zar (radhiyallahu ‘anhu) could advance forward and lead the jamaat. Hazrat Abu Zar (radhiyallahu ‘anhu), however, refused and said, “Go forward and lead the salaah as I have been commanded to listen and obey, even if it be before an Abyssinian slave, and you are an Abyssinian slave.”

(Ibn Sa’d 4/171, Siyar A’laam min Nubalaa 3/389)