Ibn ‘Abbas (May Allah be pleased with them) reported: The Messenger of Allah (peace be upon him) said,
“Do not observe Saum (fasting) before the advent of Ramadan. Observe Saum at sighting of the crescent of Ramadan and terminate it at sighting the crescent (of Shawwal). If the sky is overcast, complete (the month as) thirty (days).”
(Riyad as-Salihin , Book 9, Hadith 235)
