صحيح مسلم
Sahih Muslim
كتاب الصيام
The Book of Fasting
باب وُجُوبِ صَوْمِ رَمَضَانَ لِرُؤْيَةِ الْهِلاَلِ وَالْفِطْرِ لِرُؤْيَةِ الْهِلاَلِ وَأَنَّهُ إِذَا غُمَّ فِي أَوَّلِهِ أَوْ آخِرِهِ أُكْمِلَتْ عِدَّةُ الشَّهْرِ ثَلاَثِينَ يَوْمًا:
Chapter: The obligation to fast Ramadan when the crescent is sighted, and to break the fast when the crescent is sighted, and that if it is cloudy at the beginning or end of the month, then the month should be completed as thirty days.
Hadith 1081
This hadith is listed as number 2514 in Maktaba Shamila
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى ، أَخْبَرَنَا إِبْرَاهِيمُ بْنُ سَعْدٍ ، عَنْ ابْنِ شِهَابٍ ، عَنْ سَعِيدِ بْنِ الْمُسَيِّبِ ، عَنْ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ ، قَالَ : قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ : " إِذَا رَأَيْتُمُ الْهِلَالَ فَصُومُوا ، وَإِذَا رَأَيْتُمُوهُ فَأَفْطِرُوا ، فَإِنْ غُمَّ عَلَيْكُمْ فَصُومُوا ثَلَاثِينَ يَوْمًا " .
Abu Hurairah (RA) reported Allah's Messenger (ﷺ) as saying: Whenever you sight the new moon (of the month of Ramadan) observe fast. and when you sight it (the new moon of Shawwal) break it, and if the sky is cloudy for you, then observe fast for thirty days.
