Abdullah bin al-Samit narrates from Sayyiduna Abu Dharr (may Allah be pleased with him) that he reached al-Rabadhah when the iqamah for the prayer had already been called, and a slave was leading them. It was said: "This is Abu Dharr (may Allah be pleased with him)." So he began to step back, and Abu Dharr (may Allah be pleased with him) said: "My dear friend (peace and blessings be upon him) advised me with three things: that I listen and obey, even if it is an Abyssinian slave with mutilated limbs."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5119