Sahih Muslim 2321 a
Masruq reported:
We went to Abdullah b. 'Amr when Mu'dwiya came to Kufa, and he made a mention of Allah's Messenger (ﷺ) and said: He was never immoderate in his talk and he never reviled others. Allah's Messenger (ﷺ) also said: The best amongst you are those who are best in morals. Uthman said: When he came to Kufa along with Mu'awiya... (The rest of the hadith is the same).
حَدَّثَنَا زُهَيْرُ بْنُ حَرْبٍ، وَعُثْمَانُ بْنُ أَبِي شَيْبَةَ، قَالاَ حَدَّثَنَا جَرِيرٌ، عَنِ الأَعْمَشِ،
 عَنْ شَقِيقٍ، عَنْ مَسْرُوقٍ، قَالَ دَخَلْنَا عَلَى عَبْدِ اللَّهِ بْنِ عَمْرٍو حِينَ قَدِمَ مُعَاوِيَةُ إِلَى الْكُوفَةِ
 فَذَكَرَ رَسُولَ اللَّهِ صلى الله عليه وسلم فَقَالَ لَمْ يَكُنْ فَاحِشًا وَلاَ مُتَفَحِّشًا ‏.‏ وَقَالَ قَالَ رَسُولُ
 اللَّهِ صلى الله عليه وسلم ‏
"‏ إِنَّ مِنْ خِيَارِكُمْ أَحَاسِنَكُمْ أَخْلاَقًا ‏"‏ ‏.‏ قَالَ عُثْمَانُ حِينَ قَدِمَ
 مَعَ مُعَاوِيَةَ إِلَى الْكُوفَةِ ‏.‏