Language:
كتاب الكسوف
16  
Eclipses
(16)
Chapter: The saying of Amma ba'du during the Khutba of the eclipse
(16)
باب قَوْلِ الإِمَامِ فِي خُطْبَةِ الْكُسُوفِ أَمَّا بَعْدُ
Sahih al-Bukhari 1061
And this was narrated by Asma' who said, "Allah's Messenger (ﷺ) finished the eclipse prayer and by then the sun (eclipse) had cleared. Then he delivered the Khutba (religious talk) and praised Allah as He deserved and then said Amma ba'du."
وَقَالَ أَبُو أُسَامَةَ حَدَّثَنَا هِشَامٌ، قَالَ أَخْبَرَتْنِي فَاطِمَةُ بِنْتُ الْمُنْذِرِ، عَنْ أَسْمَاءَ، قَالَتْ فَانْصَرَفَ رَسُولُ اللَّهِ صلى الله عليه وسلم وَقَدْ تَجَلَّتِ الشَّمْسُ فَخَطَبَ، فَحَمِدَ اللَّهَ بِمَا هُوَ أَهْلُهُ ثُمَّ قَالَ ‏ "‏ أَمَّا بَعْدُ ‏"‏‏.‏
Reference : Sahih al-Bukhari 1061
In-book reference : Book 16, Hadith 20
USC-MSA web (English) reference : Vol. 2, Book 18, Hadith 168
  (deprecated numbering scheme)