‘Abdullah bin Mubaarak (rahimahullah) narrates the following:

I once said to Sufyaan Thowri (rahimahullah), “O Abu ‘Abdillah! I notice that Abu Hanifah (rahimahullah) exercises extreme caution in refraining from gheebah (backbiting)! I never heard him even speak ill of his enemies!” Sufyaan (rahimahullah) replied, “He is intelligent enough to not carry out such an action that will cause him to lose all his good deeds.”

(Wafayaat-ul-A’yaan 5/411)