Allah, Exalted is He, decreed that the sighting of the new moon (crescent) should be usedto determine the timings of the lunar months. The sighting of the crescent marks the end of one lunar month and the beginning of another. Based on this sighting, many religious obligations are determined, such as fasting and Hajj. In this hadeeth, ‘AbdullahIbn ‘Umar (may Allah be pleased with him) related that the Messenger of Allah ﷺ told them that the lunar months generally alternate between 29 and 30 days. He ﷺ said: “The (lunar) month (may be) thus and thus,” holding up his hands with all their fingers twice, but at the third time withdrawing or folding his left thumb (indicating that the month might consist of twenty-nine days). The use of sign language is the best way to explain the correct meaning, because it is more tangible and leaves no possibility of incorrect assumptions. To sum up, determining the end of the current lunar month and the beginning of the following month requires the sighting of the crescent; if the crescent is sighted on the eve of the twenty-ninth day, then the month will have ended, and that night will be the first night of the new month, and if the crescent is not sighted for some reason - such as clouds and the like - then the month is thirty days. It is deduced from the hadeeth that it is allowable to use sign language to explain an intended meaning. It is also inferred that it is not allowable to rely on means other than the sighting of the new moon to determine the beginning and end of lunar months, such as astronomical calculation. .