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.  

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

" I said to Qatada: Did you hear it from Anas? He replied in the affir- mative and added: We had inquired of him about it."  

حَدَّثَنَا شُعْبَةُ فِي هَذَا الإِسْنَادِ وَزَادَ قَالَ شُعْبَةُ فَقُلْتُ لِقَتَادَةَ أَسَمِعْتَهُ مِنْ أَنَسٍ قَالَ نَعَمْ نَحْنُ سَأَلْنَاهُ عَنْهُ  

'Umar b. al-Khattab used to recite loudly these words: Subhanak Allahumma wa bi hamdika wa tabarakasmuka wa ta'ala jadduka wa la ilaha ghairuka [Glory to Thee,0 Allah, and Thine is the Praise, and Blessed is Thy Name. and Exalted is Thy Majesty. and there is no other object of worship beside Thee]. Qatada informed in writing that Anas b. Malik had narrated to him: I observed prayer behind the Messenger of Allah ﷺ and Abu Bakr and Umar and 'Uthman. They started (loud recitation) with: AI-hamdu lillahi Rabb al-'Alamin [All Praise is due to Allah, the Lord of the worlds] and did not recite Bismillah ir- Rahman-ir-Rahim (loudly) at the beginning of the recitation or at the end of it.  

أَنَّهُ حَدَّثَهُ قَالَ صَلَّيْتُ خَلْفَ النَّبِيِّ ﷺ وَأَبِي بَكْرٍ وَعُمَرَ وَعُثْمَانَ فَكَانُوا يَسْتَفْتِحُونَ بِ { الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ} لاَ يَذْكُرُونَ بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيمِ فِي أَوَّلِ قِرَاءَةٍ وَلاَ فِي آخِرِهَا  

It is reported on the authority of Abu Talha that he had heard Anas b. Malik narrating this.  

أَنَّهُ سَمِعَ أَنَسَ بْنَ مَالِكٍ يَذْكُرُ ذَلِكَ