It was narrated from Ibn 'Umar that the Prophet (ﷺ) said: "The month is like this," and (one of the narrators) Shubah did the same gesture as Jabalah had done, copying, Ibn 'Umar: "It is twenty-nine, as he gestured twice with all fingers of both hands, and putting down one of his fingers the third time."
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا خَالِدٌ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنْ جَبَلَةَ بْنِ سُحَيْمٍ، عَنِ ابْنِ عُمَرَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " الشَّهْرُ هَكَذَا " . وَوَصَفَ شُعْبَةُ عَنْ صِفَةِ جَبَلَةَ عَنْ صِفَةِ ابْنِ عُمَرَ أَنَّهُ تِسْعٌ وَعِشْرُونَ فِيمَا حَكَى مِنْ صَنِيعِهِ مَرَّتَيْنِ بِأَصَابِعِ يَدَيْهِ وَنَقَصَ فِي الثَّالِثَةِ إِصْبَعًا مِنْ أَصَابِعِ يَدَيْهِ .
sunnah.com