question #1 Sahih al-Bukhari 1907, Book 30, Hadith 17 : How is the beginning of the fasting month determined in Islam?

Allah’s Messenger (ﷺ) said, “The month (can be) 29 nights (i.e. days), and do not fast till you see the moon,
and if the sky is overcast, then complete Sha’ban as thirty days.”