Sahih al-Bukhari 1061
Sahih al-Bukhari · Book 16: Eclipses · The saying of Amma ba'du during the Khutba of the eclipse
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 " .
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."