Sahih Muslim 2506
صحيح مسلم#2506Sahihحَدَّثَنَا هَارُونُ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا رَوْحُ بْنُ عُبَادَةَ، حَدَّثَنَا زَكَرِيَّاءُ بْنُ إِسْحَاقَ، حَدَّثَنَا عَمْرُو بْنُ دِينَارٍ، أَنَّهُ سَمِعَ ابْنَ عُمَرَ، - رضى الله عنهما - يَقُولُ سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقُولُ " الشَّهْرُ هَكَذَا وَهَكَذَا وَهَكَذَا " . وَقَبَضَ إِبْهَامَهُ فِي الثَّالِثَةِ .
Ibn Umar (Allah be pleased with both of them) reported Allah's Messenger (ﷺ) as saying:The month is thus and thus and thus (i. e. pointing with his fingers thrice), and he held back his thumb at the third time (in order to show that it can also consist of twenty-nine days)
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: 13:12