(a) Nafi' narrates from the muezzin of Sayyiduna Umar (may Allah be pleased with him), who was called Masruh, that he gave the adhan before the morning, so Sayyiduna Umar (may Allah be pleased with him) ordered him, and he narrated the hadith like the narration of Hammad bin Salamah.
(b) It is narrated from Sayyiduna Umar bin al-Khattab (may Allah be pleased with him): Give the adhan for the morning early, so that the night traveller may set out and the one at home may go out. Imam Abu Dawud (may Allah have mercy on him) says: Hammad bin Zayd narrated from Ubaydullah bin Umar, from Nafi' or someone else, that Sayyiduna Umar (may Allah be pleased with him) had an appointed muezzin whose name was Masruh or someone else.
(c) Al-Darawardi narrated from Ubaydullah bin Umar, from Nafi', from Sayyiduna Ibn Umar (may Allah be pleased with them both), that Sayyiduna Umar (may Allah be pleased with him) had a muezzin whose name was Mas'ud. He also narrated it like the previous narration.
(d) Imam Abu Dawud (may Allah have mercy on him) says: This narration concerning Sayyiduna Umar (may Allah be pleased with him) is more authentic.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1801