It is narrated from Sayyiduna Ibn Mas'ud (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Let not the adhan of Bilal (may Allah be pleased with him) - or he said: the call of Bilal (may Allah be pleased with him) - prevent any one of you from his sahur, for he gives the adhan - or he said: he calls out - so that the one standing (in prayer) may return and the one sleeping may be woken." Then he said: "It is not that he says like this, or like this, until he says like this (i.e., he described the manner)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1789
It is narrated from Sayyidah Aishah (may Allah be pleased with her) and Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) had two muezzins, Bilal and Ibn Umm Maktum (may Allah be pleased with them both). 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 gives the adhan." Al-Qasim said: There was no more between their two adhans than that this one would come down and that one would go up.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1790
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
Khubayb bin Abd al-Rahman narrates from his aunt Unaysah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) said: "When Ibn Umm Maktum (may Allah be pleased with him) gives the adhan at night, eat and drink until Bilal (may Allah be pleased with him) gives the adhan."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1792