question #3 Sahih Muslim 1081a, Book 13, Hadith 20 : What is the prescribed duration of fasting if the new moon is not sighted due to cloudy weather?

Whenever you sight the new moon (of the month of Ramadan) observe fast. and when you sight it (the new moon of Shawwal) break it, and if the sky is cloudy for you, then observe fast for thirty days.