Sufyan on Manners: The predecessors studied manners first

Abu Nu’aym reported: Sufyān al-Thawri, may Allah have mercy on him, would say, “If a man intended to write the prophetic traditions (hadith), he would study good manners and worship for twenty years before doing so.”

Source: Hilyat al-Awliyā’ 361

عن أبي النعيم عن سفيان الثوري رحمه الله قال كَانَ الرَّجُلُ إِذَا أَرَادَ أَنْ يَكْتُبَ الْحَدِيثَ تَأَدَّبَ وَتَعَبَّدَ قَبْلَ ذَلِكَ بِعِشْرِينَ سَنَةً

361 حلية الأولياء لأبي نعيم سفيان الثوري