282- وبه: أن رسول الله صلى الله عليه وسلم قال: ”الشهر تسع وعشرون، فلا تصوموا حتى تروا الهلال، ولا تفطروا حتى تروه، فإن غم عليكم فاقدروا له .“
And with this chain (it is narrated from Sayyiduna Ibn Umar, may Allah be pleased with them both) that the Messenger of Allah, peace and blessings be upon him, said: "The month is twenty-nine (29) days, so do not fast until you see the crescent, and do not break the fast (for Eid) until you see the crescent. Then if the weather is cloudy for you, complete (thirty days)."
Related hadith on this topic