(29) باب مَنْ قَالَ فِي الْخُطْبَةِ بَعْدَ الثَّنَاءِ أَمَّا بَعْدُ
Narrated Al-Miswar bin Makhrama:
Once Allah's Messenger (ﷺ) got up for delivering the Khutba and I heard him after "Tashah-hud" saying "Amma ba'du."
Reference: Sahih al-Bukhari 926
In-book reference: Book 11, Hadith 50
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 2, Book 13, Hadith 48