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
tirmidhi:396 – Aḥmad b. Manīʿ > Ismāʿīl b. Ibrāhīm > Hishām al-Dastawāʾī > Yaḥyá b. Abū Kathīr > ʿIyāḍ / Ibn Hilāl

"I said to Abu Sa'eed: 'One of us performs Salat and we do not know how (much) we prayed.' So he said: 'Messenger of Allah (S) said: "When one of you performs Salat and he does now know how (much) he prayed then let him perform two prostrations while he is sitting."  

الترمذي:٣٩٦ – حَدَّثَنَا أَحْمَدُ بْنُ مَنِيعٍ حَدَّثَنَا إِسْمَاعِيلُ بْنُ إِبْرَاهِيمَ حَدَّثَنَا هِشَامٌ الدَّسْتَوَائِيُّ عَنْ يَحْيَى بْنِ أَبِي كَثِيرٍ عَنْ عِيَاضٍ يَعْنِي ابْنَ هِلاَلٍ قَالَ

قُلْتُ لأَبِي سَعِيدٍ أَحَدُنَا يُصَلِّي فَلاَ يَدْرِي كَيْفَ صَلَّى فَقَالَ قَالَ رَسُولُ اللَّهِ ﷺ إِذَا صَلَّى أَحَدُكُمْ فَلَمْ يَدْرِ كَيْفَ صَلَّى فَلْيَسْجُدْ سَجْدَتَيْنِ وَهُوَ جَالِسٌ قَالَ وَفِي الْبَابِ عَنْ عُثْمَانَ وَابْنِ مَسْعُودٍ وَعَائِشَةَ وَأَبِي هُرَيْرَةَ  

قَالَ أَبُو عِيسَى حَدِيثُ أَبِي سَعِيدٍ حَدِيثٌ حَسَنٌ وَقَدْ رُوِيَ هَذَا الْحَدِيثُ عَنْ أَبِي سَعِيدٍ مِنْ غَيْرِ هَذَا الْوَجْهِ وَقَدْ رُوِيَ عَنِ النَّبِيِّ ﷺ أَنَّهُ قَالَ إِذَا شَكَّ أَحَدُكُمْ فِي الْوَاحِدَةِ وَالثِّنْتَيْنِ فَلْيَجْعَلْهُمَا وَاحِدَةً وَإِذَا شَكَّ فِي الثِّنْتَيْنِ وَالثَّلاَثِ فَلْيَجْعَلْهُمَا ثِنْتَيْنِ وَيَسْجُدْ فِي ذَلِكَ سَجْدَتَيْنِ قَبْلَ أَنْ يُسَلِّمَ وَالْعَمَلُ عَلَى هَذَا عِنْدَ أَصْحَابِنَا وَقَالَ بَعْضُ أَهْلِ الْعِلْمِ إِذَا شَكَّ فِي صَلاَتِهِ فَلَمْ يَدْرِ كَمْ صَلَّى فَلْيُعِدْ

See similar narrations below:

Collected by Ibn Mājah, Nasāʾī's Kubrá
ibnmajah:1204 – ʿAmr b. Rāfiʿ > Ismāʿīl Ibn ʿUlayyah > Hishām > Yaḥyá > ʿIyāḍ

“One of us prays and he does not know how many (Rak’ah) he has prayed.” He said: “The Messenger of Allah ﷺ said: ‘When anyone of you prays and does not know how many he has prayed, let him perform two prostrations while he is sitting.’”  

ابن ماجة:١٢٠٤ – حَدَّثَنَا عَمْرُو بْنُ رَافِعٍ حَدَّثَنَا إِسْمَاعِيلُ ابْنُ عُلَيَّةَ عَنْ هِشَامٍ حَدَّثَنِي يَحْيَى حَدَّثَنِي عِيَاضٌ أَنَّهُ سَأَلَ أَبَا سَعِيدٍ الْخُدْرِيَّ فَقَالَ

أَحَدُنَا يُصَلِّي فَلاَ يَدْرِي كَمْ صَلَّى فَقَالَ قَالَ رَسُولُ اللَّهِ ﷺ إِذَا صَلَّى أَحَدُكُمْ فَلَمْ يَدْرِ كَمْ صَلَّى فَلْيَسْجُدْ سَجْدَتَيْنِ وَهُوَ جَالِسٌ  

nasai-kubra:590 – Ismāʿīl b. Masʿūd > Khālid / Ibn al-Ḥārith > Hishām > al-Dastuwāʾī > Yaḥyá > Ibn Abū Kathīr > ʿIyāḍ

“One of us prays and he does not know how many (Rak’ah) he has prayed.” He said: “The Messenger of Allah ﷺ said: ‘When anyone of you prays and does not know how many he has prayed, let him perform two prostrations while he is sitting.’” (Using translation from Ibn Mājah 1204)   

الكبرى للنسائي:٥٩٠ – أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ قَالَ حَدَّثَنَا خَالِدٌ يَعْنِي ابْنَ الْحَارِثِ قَالَ حَدَّثَنَا هِشَامٌ هُوَ الدَّسْتُوَائِيُّ عَنْ يَحْيَى هُوَ ابْنُ أَبِي كَثِيرٍ عَنْ عِيَاضٍ قَالَ

سَأَلْتُ أَبَا سَعِيدٍ الْخُدْرِيِّ قُلْتُ يُصَلِّي أَحَدُنَا فَلَا يَدْرِي كَمْ صَلَّى؟ قَالَ قَالَ رَسُولُ اللهِ ﷺ «إِذَا صَلَّى أَحَدُكُمْ فَلَمْ يَدْرِ كَمْ صَلَّى فَلْيَسْجُدْ سَجْدَتَيْنِ وَهُوَ جَالِسٌ»