Sunan an-Nasa'i, Book 11, Hadith 33 (In-Book) ⓘ
Ibn Abdullah bin Mughaffal said: "If Abdullah bin Mughaffal heard any one of us recite: 'In the Name of Allah, the Most Gracious, the Most Merciful', he would say: 'I prayed behind the Messenger of Allah and behind Abu Bakr and behind Umar-may Allah be pleased with them both- and I did not hear any of them recite: 'In the Name of Allah, the Most Gracious, the Most Merciful."
أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ، قَالَ حَدَّثَنَا خَالِدٌ، قَالَ حَدَّثَنَا عُثْمَانُ بْنُ غِيَاثٍ، قَالَ أَخْبَرَنِي أَبُو نُعَامَةَ الْحَنَفِيُّ، قَالَ حَدَّثَنَا ابْنُ عَبْدِ اللَّهِ بْنِ مُغَفَّلٍ، قَالَ كَانَ عَبْدُ اللَّهِ بْنُ مُغَفَّلٍ إِذَا سَمِعَ أَحَدَنَا، يَقْرَأُ { بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيمِ } يَقُولُ صَلَّيْتُ خَلْفَ رَسُولِ اللَّهِ صلى الله عليه وسلم وَخَلْفَ أَبِي بَكْرٍ وَخَلْفَ عُمَرَ رضى الله عنهما فَمَا سَمِعْتُ أَحَدًا مِنْهُمْ قَرَأَ بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيمِ .
also referenced under: Hadith 908 (Reference) & Volume 2, Book 11, Hadith 909 (DarusSalam)