Sahih Muslim 2510
صحيح مسلم#2510Sahihوَحَدَّثَنَا 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 .
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
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 13:16