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 1080
This hadith is listed as number 2498 in Maktaba Shamila
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى ، قَالَ : قَرَأْتُ عَلَى مَالِكٍ ، عَنْ نَافِعٍ ، عَنْ ابْنِ عُمَرَ رَضِيَ اللَّهُ عَنْهُمَا ، عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَنَّهُ ذَكَرَ رَمَضَانَ ، فَقَالَ : " لَا تَصُومُوا حَتَّى تَرَوْا الْهِلَالَ ، وَلَا تُفْطِرُوا حَتَّى تَرَوْهُ ، فَإِنْ أُغْمِيَ عَلَيْكُمْ ، فَاقْدِرُوا لَهُ " .
Ibn 'Umar (RA) (Allah be pleased with both of them) reported Allah's Messenger (ﷺ) as saying in connection with Ramadan: Do not fast till you see the new moon, and do not break fast till you see it; but if the weather is cloudy calculate about it.
