Musannaf Ibn Abi Shaybah 38490 — the first to do a thing, and who did

Abd al-Rahman bin Ka'b bin Malik said: When my father lost his sight, I used to take him to the Friday prayer. When he heard the Friday adhan, he would seek forgiveness for Sayyiduna Abu Umamah As'ad bin Zurarah (may Allah be pleased with him) and supplicate for him. I asked him: "O my father, why do you supplicate and seek forgiveness for Abu Umamah on Friday?" He said: "My son, before the Prophet (peace and blessings be upon him) came (to Madinah), he was the first to lead us in the Friday prayer, by the spring and pasture of Banu Bayadah." I asked: "How many men were you at that time?" He said: "At that time we were forty men."