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
nasai-kubra:980 – Muḥammad b. ʿAlī b. al-Ḥasan b. Shaqīq from my father > Abū Ḥamzah > Manṣūr b. Zādhān > Anas b. Mālik

"The Messenger of Allah ﷺ led us in prayer, and we did not hear him recite: In the Name of Allah, the Most Gracious, the Most Merciful. And Abu Bakr and Umar led us in prayer and we did not hear it from them either." (Using translation from Nasāʾī 906)  

الكبرى للنسائي:٩٨٠ – أَخْبَرَنَا مُحَمَّدُ بْنُ عَلِيِّ بْنِ الْحَسَنِ بْنِ شَقِيقٍ قَالَ سَمِعْتُ أَبِي يَقُولُ أَخْبَرَنَا أَبُو حَمْزَةَ عَنْ مَنْصُورِ بْنِ زَاذَانَ عَنْ أَنَسِ بْنِ مَالِكٍ قَالَ

«صَلَّى بِنَا رَسُولُ اللهِ ﷺ فَلَمْ يُسْمِعْنَا قِرَاءَةَ بِسْمِ اللهِ الرَّحْمَنِ الرَّحِيمِ وَصَلَّى بِنَا أَبُو بَكْرٍ وَعُمَرُ فَلَمْ نَسْمَعْهَا مِنْهُمَا»  

See similar narrations below:

Collected by Muslim, Nasāʾī
muslim:399a – Muḥammad b. al-Muthanná And Ibn Bashhār > Ghundar > Ibn al-Muthanná > Muḥammad b. Jaʿfar > Shuʿbah > Qatādah > Anas

I observed prayer along with the Messenger of Allah ﷺ and with Abu Bakr, Umar and Uthman (may Allah be pleased with all of them), but I never heard any one of them reciting Bismillah-ir-Rahman-ir-Rahim loudly.  

مسلم:٣٩٩a – حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى وَابْنُ بَشَّارٍ كِلاَهُمَا عَنْ غُنْدَرٍ قَالَ ابْنُ الْمُثَنَّى حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ حَدَّثَنَا شُعْبَةُ قَالَ سَمِعْتُ قَتَادَةَ يُحَدِّثُ عَنْ أَنَسٍ قَالَ

صَلَّيْتُ مَعَ رَسُولِ اللَّهِ ﷺ وَأَبِي بَكْرٍ وَعُمَرَ وَعُثْمَانَ فَلَمْ أَسْمَعْ أَحَدًا مِنْهُمْ يَقْرَأُ {بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيمِ}  

nasai:906 – Muḥammad b. ʿAlī b. al-Ḥasan b. Shaqīq from my father > Abū Ḥamzah > Manṣūr b. Zādhān > Anas b. Mālik

"The Messenger of Allah ﷺ led us in prayer, and we did not hear him recite: In the Name of Allah, the Most Gracious, the Most Merciful. And Abu Bakr and Umar led us in prayer and we did not hear it from them either."  

النسائي:٩٠٦ – أَخْبَرَنَا مُحَمَّدُ بْنُ عَلِيِّ بْنِ الْحَسَنِ بْنِ شَقِيقٍ قَالَ سَمِعْتُ أَبِي يَقُولُ أَنْبَأَنَا أَبُو حَمْزَةَ عَنْ مَنْصُورِ بْنِ زَاذَانَ عَنْ أَنَسِ بْنِ مَالِكٍ قَالَ

صَلَّى بِنَا رَسُولُ اللَّهِ ﷺ فَلَمْ يُسْمِعْنَا قِرَاءَةَ { بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيمِ } وَصَلَّى بِنَا أَبُو بَكْرٍ وَعُمَرُ فَلَمْ نَسْمَعْهَا مِنْهُمَا