It is narrated from Sayyiduna Salman al-Farisi (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Let the call of Bilal not keep any of you from his pre-dawn meal (suhur), for Bilal calls the adhan only so that the one standing in prayer may return and the one asleep may wake up."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6110