Al-Adab Al-Mufrad, Hadith 1121 ⓘ
Hisham ibn 'Urwa said, "I saw some of the letters of the Prophet, may Allah bless him and grant him peace. After the introduction he said, 'Following on from that'"
حَدَّثَنَا رَوْحُ بْنُ عَبْدِ الْمُؤْمِنِ، قَالَ: حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ هِشَامِ بْنِ عُرْوَةَ قَالَ: رَأَيْتُ رَسَائِلَ مِنْ رَسَائِلِ النَّبِيِّ صلى الله عليه وسلم، كُلَّمَا انْقَضَتْ قِصَّةٌ قَالَ: أَمَّا بَعْدُ.
also referenced under: Book 45, Hadith 5 (In-Book) & Book 45, Hadith 1121 (English)