Musannaf Ibn Abi Shayba 17:883

Abu Bakr narrated to us, he said: Ibn ‘Uyaynah narrated to us, from Dawud ibn Shabur, from Mujahid, who said: We used to boast over the people with four: with our jurist, our storyteller, our caller to prayer (mu'adhdhin), and our reciter. Our jurist was Ibn ‘Abbas, our caller to prayer was Abu Mahdhurah, our storyteller was ‘Ubayd ibn ‘Umayr, and our reciter was ‘Abdullah ibn al-Sa’ib.