Sayyiduna Abu Hurairah (may Allah be pleased with him) narrated that the Prophet Muhammad (peace and blessings be upon him) said, or he said that Abu al-Qasim (peace and blessings be upon him) said: "Begin fasting upon sighting the moon and end fasting upon sighting the moon, and if it is cloudy, then complete thirty days."
Hadith Referenceاللؤلؤ والمرجان / كتاب الصيام / 656
Hadith Gradingمحدثین:«صحیح»
Hadith Takhrij«صحیح، أخرجه البخاري في: 30 كتاب الصوم: 11 باب قول النبي صلی اللہ علیہ وسلم إذا رأيتم الهلال فصوموا وإذا رأيتموه فأفطروا»