Anas bin Malik reported,
The last time I looked at the Messenger of Allah ﷺ, he drew back the curtain while the people stood in rows behind Abu Bakr 
. Abu Bakr wanted to step back, but the Prophet motioned to them to remain in place. Then he let the curtain fall. He passed away by the end of that day, and it was a Monday.
Nasai 1832
Sahihأخبرنا قتيبة قال حدثنا سفيان عن الزهري
عن أنس قال
آخر نظرة نظرتها إلى رسول الله ﷺ كشف الستارة والناس صفوف خلف أبي بكر رضي الله عنه فأراد أبو بكر أن يرتد فأشار إليهم أن امكثوا وألقى السجف وتوفي من آخر ذلك اليوم وذلك يوم الاثنين
Muslim narrated it in the Book of Prayer, in the chapter "The Imam Appointing a Deputy When Prevented by Illness, Travel, etc.," hadith 419/99, from the hadith of Sufyan bin Uyayna. Bukhari and others also narrated it in "Who Leads the People in Prayer, etc.," hadith 754, from the hadith of Zuhri, with the same wording. It also appears in the adhan, in the chapter "May One Turn Aside for a Matter That Arises?" hadith 1957.