It is narrated from Sayyiduna Jubair bin Mut'im (may Allah be pleased with him) that once the Prophet (peace and blessings of Allah be upon him) was on a journey. At one stop, he said, "Who will keep watch tonight so that we do not oversleep at the time of Fajr prayer?" Sayyiduna Bilal offered himself and sat facing the east. The people fell asleep unaware, and it was the heat of the sun that woke them up. They quickly got up, departed from that place, performed ablution, Sayyiduna Bilal gave the call to prayer, the people prayed the two Sunnah units, and then performed the Fajr prayer.