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Observe fast on sighting it (the new moon) and break it on sighting it. But if (due to clouds) the actual position of the month is concealed from you, you should then count thirty (days).

the Prophet (ﷺ) said: "Do not precede the month with a day nor with two days, unless that fast falls on a day that one of you would have (normally) fasted. Fast with its sighting and break fast with its sighting, and if it is cloudy, then c

"the Messenger of Allah said: 'Fast when you see it and stop fasting when you see it, and if it is obscured from you (too cloudy), then count it as thirty (days). "'

"Fast when you see it and break the fast when you see it. And if it is too cloudy, complete the number [of days in the month] as thirty. And do not anticipate the month." Hatim said: i.e., the number of days in Sha"ban.