I heard Abu Qasim ﷺ say, "The best among you are those with the finest character, when they have understanding of the religion."
سمعت أبا القاسم ﷺ يقول: خياركم أحاسنكم أخلاقا إذا فقهوا.
Ahmad (10022) and Bukhari in Adab al-Mufrad (285) both narrated it through Hammad bin Salama, from Muhammad bin Ziyad, from Abu Hurairah, who mentioned it. Its chain of transmission is sahih.