It is narrated from Sayyiduna Ibn Mas'ud (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) was returning from Hudaybiyyah at night, and we camped on soft ground. The Prophet (peace be upon him) said: "Who will keep watch over us? (Who will wake us up for Fajr?)" Sayyiduna Bilal (may Allah be pleased with him) offered himself. The Prophet (peace be upon him) said: "What if you also fall asleep?" He replied: "I will not sleep." Coincidentally, he too fell asleep until the sun had risen and so-and-so companions woke up, among them was Sayyiduna Umar (may Allah be pleased with him). He woke everyone up, and the Prophet (peace be upon him) also woke up and said: "Do as you used to do" (perform the prayer as usual). When the people had done so, he said: "If any of you sleeps or forgets, then do likewise."