Sayyiduna Amr bin Abasah (may Allah be pleased with him) said that he came to the Prophet (peace and blessings be upon him) in Makkah. I said: Who are you? He (peace and blessings be upon him) said: "I am called a prophet." I said: And what is a prophet? He (peace and blessings be upon him) said: "Allah has sent me as a messenger." I said: With what has He sent you? He (peace and blessings be upon him) said: "Allah has sent me with joining the ties of kinship, breaking the idols, and that He be affirmed as One, with nothing associated with Him." I said: Who is with you? He (peace and blessings be upon him) said: "A free man and a slave." Sayyiduna Amr (may Allah be pleased with him) said: With him (peace and blessings be upon him) on that day were Sayyiduna Abu Bakr and Sayyiduna Bilal (may Allah be pleased with them both), who had believed in him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 13095