Habib bin Abd al-Rahman narrates: I heard my paternal aunt, who had the honour of performing Hajj with the Prophet (peace and blessings be upon him), say: The Prophet (peace and blessings be upon him) used to say: "Ibn Umm Maktum gives the call to prayer (adhan) while it is still night (that is, shortly before true dawn), so keep eating and drinking until Bilal gives the call to prayer." (The narrator is unsure; perhaps the words are:) "Bilal gives the call to prayer while it is still night, so keep eating and drinking until Ibn Umm Maktum gives the call to prayer." The female narrator says: (The gap between the calls of the two of them was such) that one would be going up while the other was coming down, and we would say to him: "Wait a little, so that we may take our pre-dawn meal (suhur)."
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصيام / 4861