The Messenger of Allah ﷺ said, "The most complete of believers in faith are those with the best character."
حدثنا أحمد بن حنبل حدثنا يحيى بن سعيد عن محمد بن عمرو عن أبي سلمة
قال رسول الله ﷺ أكمل المؤمنين إيمانا أحسنهم خلقا
[Its isnad is hasan] Tirmidhi narrated it in the chapter on breastfeeding, in the section on what has been mentioned regarding a woman's right over her husband, no. 1162, from the hadith of Muhammad bin Amr Laythi through this route. Ibn Hibban graded it sahih, no. 1926, as did Hakim, 3/1, and Dhahabi agreed with him. It is also found in Musnad Ahmad, 2/472.