(a) Muhammad bin Yahya said: The hadith of Hammad bin Salamah from Ayyub from Nafi' from Sayyiduna Ibn Umar (may Allah be pleased with them both), that Bilal (may Allah be pleased with him) gave the adhan before the break of dawn, is shadh (anomalous) and does not sit well with the heart; it is contrary to what people narrate from Sayyiduna Ibn Umar (may Allah be pleased with them both).
(b) The Shaykh says that Ma'mar bin Rashid narrated it from Ayyub, that Sayyiduna Bilal (may Allah be pleased with him) once gave the adhan at night, and he narrated it as mursal. It is also narrated from Abd al-Aziz bin Abi Rawwad from Nafi' as a connected narration, and it is da'if (weak) and not authentic.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1799