Translation
(26) Knowledge (Kitab Al-Ilm)
كتاب العلم
(3) Chapter: Writing knowledge
(3) باب فِي كِتَابَةِ الْعِلْمِ
Sunan Abi Dawud 3650 
Al-Walid said :
I asked Abu `Amr: What are they writing? He said: The sermon which he heard that day.
حَدَّثَنَا عَلِيُّ بْنُ سَهْلٍ الرَّمْلِيُّ، قَالَ حَدَّثَنَا الْوَلِيدُ، قَالَ قُلْتُ لأَبِي عَمْرٍو مَا يَكْتُبُوهُ قَالَ الْخُطْبَةَ الَّتِي سَمِعَهَا يَوْمَئِذٍ مِنْهُ ‏.‏
Grade :  Sahih Maqtu' (Al-Albani) صحيح مقطوع  (الألباني)حكم :
Reference : Sunan Abi Dawud 3650
In-book reference : Book 26, Hadith 10
English translation : Book 25, Hadith 3642