Abdullah bin Abbas reported,

Abu Bakr came out while Umar bin Khattab was addressing the people. He said, "Sit down, Umar."Umar refused to sit, so the people turned to Abu Bakr and left Umar.Abu Bakr said, "Now then, whoever among you used to worship Muhammad ﷺ, Muhammad has died. And whoever among you worships Allah, Allah is living and does not die. Allah has said, 'Muhammad is no more than a messenger, and messengers have passed away before him', up to His words, 'the grateful'" [Al Imran 3:144].The narrator said, By Allah, it was as though the people had not known that Allah had revealed this verse until Abu Bakr recited it. Then they all took it up from him, and I did not hear anyone among the people who was not reciting it.Saeed bin Musayab told me that Umar said, "By Allah, the moment I heard Abu Bakr recite it, I was stunned, my legs could no longer hold me, and I sank to the ground. When I heard him recite it, I knew that the Prophet ﷺ had died."

Bukhari 4454

Sahih

قال الزهري وحدثني أبو سلمة

عن عبد الله بن عباس

أن أبا بكر خرج وعمر بن الخطاب يكلم الناس فقال اجلس يا عمر فأبى عمر أن يجلس فأقبل الناس إليه وتركوا عمر فقال أبو بكر أما بعد فمن كان منكم يعبد محمدا ﷺ فإن محمدا قد مات ومن كان منكم يعبد الله فإن الله حي لا يموت قال الله {وما محمد إلا رسول قد خلت من قبله الرسل} إلى قوله {الشاكرين} وقال والله لكأن الناس لم يعلموا أن الله أنزل هذه الآية حتى تلاها أبو بكر فتلقاها منه الناس كلهم فما أسمع بشرا من الناس إلا يتلوها فأخبرني سعيد بن المسيب أن عمر قال والله ما هو إلا أن سمعت أبا بكر تلاها فعقرت حتى ما تقلني رجلاي وحتى أهويت إلى الأرض حين سمعته تلاها علمت أن النبي ﷺ قد مات

البخاري 4454صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Bukhari
Book
Expeditions
Chapter
Illness of the Prophet ﷺ and his death
Numbering
Darussalam 4454
Bukhari 4454