Sayyiduna Abdullah bin Umar (may Allah be pleased with them) narrates that the Messenger of Allah (peace and blessings be upon him) mentioned Ramadan and said: Do not begin fasting until you see the moon, and likewise, do not end the fast until you see the moon. And if it is cloudy, then complete thirty days.
Hadith Referenceاللؤلؤ والمرجان / كتاب الصيام / 653
Hadith Gradingمحدثین:«صحیح»
Hadith Takhrij«صحیح، أخرجه البخاري في: 30 كتاب الصوم: 11 باب قول النبي صلی اللہ علیہ وسلم إذا رأيتم الهلال فصوموا»