The Messenger of Allah (ﷺ) as saying: He who has in his heart as much pride as much pride as grain of mustard-seed will not enter paradise. And he who has in his heart as much faith as grain of mustard-seed will not enter Hell.

Abu Dawud said: Al-Qasmali has transmitted it from Al-A'mash in a similar way.
Sunan Abi Dawud Book 34, Hadith 72