Jami` at-Tirmidhi 246
جامع الترمذي#246SahihAnas narrated:"Allah's Messenger, Abu Bakr, Umar and Uthman opened the Salat with (Al-Hamdu-lillahi rabbil-alamin)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 2:98