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 2510 in Maktaba Shamila
وحَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى ، حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ ، حَدَّثَنَا شُعْبَةُ ، عَنْ عُقْبَةَ وَهُوَ ابْنُ حُرَيْثٍ ، قَالَ : سَمِعْتُ ابْنَ عُمَرَ رَضِيَ اللَّهُ عَنْهُمَا ، يَقُولُ : قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ : " الشَّهْرُ تِسْعٌ وَعِشْرُونَ " ، وَطَبَّقَ شُعْبَةُ يَدَيْهِ ثَلَاثَ مِرَارٍ ، وَكَسَرَ الْإِبْهَامَ فِي الثَّالِثَةِ ، قَالَ عُقْبَةُ : وَأَحْسِبُهُ قَالَ الشَّهْرُ ثَلَاثُونَ وَطَبَّقَ كَفَّيْهِ ثَلَاثَ مِرَارٍ .
Ibn 'Umar (Allah be pleased with both of them) reported Allah's Messenger (ﷺ) as saying: The month (of Ramadan) may consist of twenty nine days, and Shu'bah (one of the narrators) (gave a practical demonstration how the Holy prophet (ﷺ) explained to them) by unfolding his hands thrice and folding his thumb at the third turn. 'Uqba (one of the narrators in this chain of transmitters) said: I think that he said that the month consists of thirty days and unfolded his palm three times.
