Allah, Exalted is He, decreed that the sighting of the new moon (crescent) should be used to determine the timings of the lunar months. The sighting of the crescent marks the end of a lunar month and the beginning of another. Based on that sighting, many religious obligations are determined, such as fasting and Hajj. In this hadeeth, the Prophet ﷺ underlined that Muslims must not observe fasting in the month of Ramadan except after sighting the new moon after the sunset of the twenty-ninth day of Sha‘baan, and also must not end their fasting (at the end of the month) except after sighting the crescent of the month of Shawwaal after sunset on the twenty-ninth day of Ramadan. If the sighting of the new moon is not possible because of clouds, or for any given reason, the month will be considered thirty days, because the maximum length of a lunar month is thirty days, and thus it is proved with certainty that the month has begun or ended. It is also deduced from the hadeeth that it is not allowable to rely on meansother than the sighting of the new moon to determine the beginning and end of lunar months, such as the astronomical calculation. .