Sahih Muslim Book 4, Hadith 105
The Messenger of Allah (ﷺ) ordered Abu Bakr that he should lead people in prayer during his illness, and he led them in prayer. `Urwa said: The Messenger of Allah (ﷺ) felt relief and went (to the mosque) and Abu Bakr was leading the people in prayer. When Abu Bakr saw him he began to withdraw, but the Messenger of Allah (ﷺ) signaled him to remain where he was. The Messenger of Allah (ﷺ) sat opposite to Abu Bakr by his side. Abu Bakr said prayer following the prayer of the Messenger of Allah (ﷺ), and the people said prayer following the prayer of Abu Bakr.
When the Messenger of Allah (ﷺ) suffered from illness of which he died, and in the hadith transmitted by Ibn Mus-hir, the words are: The Messenger of Allah (ﷺ) was brought till he was seated by his (Abu Bakr's) side and the Apostle (ﷺ) led the people in prayer and Abu Bakr was making takbir audible to them, and in the hadith transmitted by 'Isa the (words are):" The Messenger of Allah (ﷺ) sat and led the people in prayer and Abu Bakr was by his side and he was making (takbir) audible to the people."
The Messenger of Allah (ﷺ) breathed his last on that very day.