Bukhari :: Book 3 :: Volume 31 :: Hadith 131
Narrated Abdullah bin Umar:
Allah's Apostle 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."
Source materials are from the University of Southern California MSA site|
Hadith eBooks converted from Imaan Star