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'ba (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.
وَحَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، حَدَّثَنَا شُعْبَةُ، عَنْ عُقْبَةَ، - وَهُوَ ابْنُ حُرَيْثٍ - قَالَ سَمِعْتُ ابْنَ عُمَرَ، - رضى الله عنهما - يَقُولُ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " الشَّهْرُ تِسْعٌ وَعِشْرُونَ " . وَطَبَّقَ شُعْبَةُ يَدَيْهِ ثَلاَثَ مِرَارٍ وَكَسَرَ الإِبْهَامَ فِي الثَّالِثَةِ . قَالَ عُقْبَةُ وَأَحْسِبُهُ قَالَ " الشَّهْرُ ثَلاَثُونَ " وَطَبَّقَ كَفَّيْهِ ثَلاَثَ مِرَارٍ .
Muslim
The Book of Fasting • Hadith 16