Sunan Ibn Majah, Chapter: The Chapters on Jihad

that he reached Rabadhah when the Iqamah for the prayer had already been given, and there was a slave leading them in prayer. It was said: "This is Abu Dharr," so he (the slave) started to move back. But Abu Dharr said: "My close friend (i.e., the Prophet (saw)) told me to listen and obey, even if (the leader was) an Ethiopian slave with amputated limbs."