Ibn 'Abbas said
We used to know that Allah's Messenger (ﷺ) had finished his prayer when we heard the takbir (Allah-O-Akbar).
Ibn 'Abbas reported
We knew the finishing of the prayer of the Messenger of Allah (ﷺ) through takbir. 'Amr (b. Dinar) said: I made a mention of it to Abu Mas'ud. hue he rejected it and said: I never narrated it to you. 'Amr said: He did narrate it before this.
Ibn 'Abbas reported
Dhikr (mentioning the name of Allah) in a loud voice after obligatory prayers was (a common practice) during the lifetime of the Messenger of Allah (ﷺ) ; and when I heard that I came to knew that they (the people) had finished the prayer.