It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Prophet Muhammad (peace be upon him) said: "Eat and drink (take suhoor) at the call to prayer of Bilal at night, and stop suhoor at the call to prayer of Ibn Umm Maktum."
Hadith Referenceالسنن المأثورة / باب ما جاء في الأذان / 284
Hadith Takhrijصحیح بخاری، الاذان، باب الاذان بعد الفجر، رقم : 620