Khubayb bin Abd al-Rahman says that my aunt Unaysah (may Allah be pleased with her) said: Sayyiduna Bilal and Ibn Umm Maktum (may Allah be pleased with them both) used to give the adhan for the Prophet (peace and blessings be upon him). 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 until Ibn Umm Maktum (may Allah be pleased with him) gives the adhan." We used to hold Ibn Umm Maktum (may Allah be pleased with him) back from the adhan, and we would say: Stay as you are until we have taken our sahur. And their adhans were such that this one would come down and that one would go up.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1791