Narrated `Abdullâh bin `Umar (may Allah be pleased with him): Allâh's Messenger (may
peace be upon him) said, The month can be 29 nights (i.e. days), and do not observe Saum
(fast) till you see the crescent, and if the sky is overcast, then complete the month of Sha`bân
as 30 days. (Bukhari)