Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Do not let Bilal's (may Allah be pleased with him) adhan prevent you from eating suhoor, for Bilal (may Allah be pleased with him) gives the adhan to awaken the one who is sleeping and to bring back the one who is praying (qiyam). The true Fajr is not the one that appears vertically, but rather the one that spreads horizontally (right and left)."