Sahih Muslim Book 13, Hadith 22

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).

← Previous Hadith Observe fast on sighting it (the new moon) and break (fast) on sighting it (the new moon), but if the sky is cloudy for you, then complete the number (of thirty).

Sahih Muslim Book 13, Hadith 21 Next Hadith → Observe fast when you see it (the new moon) and break fast when you see it (the new moon of Shawwal), but when (the actual position of the month is) concealed from you (on account of cloudy sky), then count thirty days.

Sahih Muslim Book 13, Hadith 23