[Machine] I prayed behind the Prophet, ﷺ , and Abu Bakr and Umar, and they used to begin with "Alhamdu lillahi" [Chapter 1, verse 2 of Al-Fatihah].
صَلَّيْتُ خَلْفَ النَّبِيِّ ﷺ وَأَبِي بَكْرٍ وَعُمَرَ فَكَانُوا يَفْتَتِحُونَ بِ {الْحَمْدُ} [الفاتحة 2]
The Prophet, Abu Bakr and ʿUmar used to start the prayer with "Al hamdu li l-lahi Rabbi l-ʿalamin (All praise is but to Allah, Lord of the Worlds).
أَنَّ النَّبِيَّ ﷺ وَأَبَا بَكْرٍ وَعُمَرَ ؓ كَانُوا يَفْتَتِحُونَ الصَّلاَةَ بِ {الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ}