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 2509 in Maktaba Shamila
وحَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ ، حَدَّثَنَا أَبِي ، حَدَّثَنَا شُعْبَةُ ، عَنْ جَبَلَةَ ، قَالَ : سَمِعْتُ ابْنَ عُمَرَ رَضِيَ اللَّهُ عَنْهُمَا ، يَقُولُ : قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ : " الشَّهْرُ كَذَا وَكَذَا وَكَذَا ، وَصَفَّقَ بِيَدَيْهِ مَرَّتَيْنِ بِكُلِّ أَصَابِعِهِمَا ، وَنَقَصَ فِي الصَّفْقَةِ الثَّالِثَةِ إِبْهَامَ الْيُمْنَى أَوِ الْيُسْرَى " .
Ibn 'Umar (RA) (Allah be pleased with both of them) reported Allah's Messenger (ﷺ) as saying: The month is thus, and thus, and thus, and he flapped his hands with all their fingers twice, but at the third turn, folded his right thumb or left thumb (in order to give an idea of twenty-nine).
