Shu'ayb bin Harb says: I said to Imam Malik bin Anas (may Allah have mercy on him): Did the Prophet (peace and blessings be upon him) not order Bilal (may Allah be pleased with him) to repeat the adhan? He said: The Messenger of Allah (peace and blessings be upon him) said: "Bilal (may Allah be pleased with him) gives the adhan at night, so eat and drink." I said: Did he (peace and blessings be upon him) not order him to repeat the adhan? He said: No, among us the adhan (for Fajr) has always been given at night.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1804