Do not fast till you see the new moon, and do not break fast till you see it; but if the weather is cloudy calculate about it.
Sahih Muslim Book 13, Hadith 4
← Previous Hadith " When (the month of) Ramadan begins."

Sahih Muslim Book 13, Hadith 3 Next Hadith → The month is thus and thus. (He then withdrew his thumb at the third time). He then said: Fast when you see it, and break your fast when you see it, and if the weather is cloudy calculate it (the months of Sha'ban and Shawwal) as thirty days.

Sahih Muslim Book 13, Hadith 5