Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī

ذِكْرُ الْإِخْبَارِ بِأَنَّ الشَّهْرَ قَدْ يَكُونُ فِي بَعْضِ الْأَحْوَالِ تِسْعًا وَعِشْرِينَ

ibnhibban:3454 – al-Faḍl b. al-Ḥubāb > Abū al-Walīd And al-Ḥawḍī > Shuʿbah > Jabalah b. Suḥaym > Raʾayt Ibn ʿUmar

The Prophet ﷺ said, "The month is like this and this," (at the same time he showed the fingers of both his hands thrice) and left out one thumb on the third time. (Using translation from Bukhārī 1908)  

ابن حبّان:٣٤٥٤ – أَخْبَرَنَا الْفَضْلُ بْنُ الْحُبَابِ حَدَّثَنَا أَبُو الْوَلِيدِ وَالْحَوْضِيُّ قَالَا حَدَّثَنَا شُعْبَةُ أَخْبَرَنِي جَبَلَةُ بْنُ سُحَيْمٍ قَالَ رَأَيْتُ ابْنَ عُمَرَ يَقُولُ

قَالَ رَسُولُ اللَّهِ ﷺ «إِنَّ الشَّهْرَ هَكَذَا وَهَكَذَا» وَخَنَسَ الْإِبْهَامَ فِي الثَّالِثَةِ  

See similar narrations below:

Collected by Bukhārī
bukhari:1908 – Abū al-Walīd > Shuʿbah > Jabalah b. Suḥaym > Ibn ʿUmar

The Prophet ﷺ said, "The month is like this and this," (at the same time he showed the fingers of both his hands thrice) and left out one thumb on the third time.  

البخاري:١٩٠٨ – حَدَّثَنَا أَبُو الْوَلِيدِ حَدَّثَنَا شُعْبَةُ عَنْ جَبَلَةَ بْنِ سُحَيْمٍ قَالَ سَمِعْتُ ابْنَ عُمَرَ ؓ يَقُولُ

قَالَ النَّبِيُّ ﷺ الشَّهْرُ هَكَذَا وَهَكَذَا وَخَنَسَ الإِبْهَامَ فِي الثَّالِثَةِ