(23) باب الذِّكْرِ بَعْدَ الصَّلاَةِ
Ibn 'Abbas said:
We used to know that Allah's Messenger (ﷺ) had finished his prayer when we heard the takbir (Allah-O-Akbar).
Reference: Sahih Muslim 583 a
In-book reference: Book 5, Hadith 154
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1209