Sunan Ibn Majah, Chapter: The Chapters on Tribulations

that the Messenger of Allah (saw) said: that the Messenger of Allah (saw) said:"No one of you should belittle himself." They said: "O Messenger of Allah, how could anyone of us belittle himself?" He said: "If he sees something concerning which he should speak out for the sake of Allah but does not say anything. Allah will say to him on the Day of Resurrection: "What prevented you from speaking concerning such and such?" He will say: "Fear of the people." (Allah) will say: "Rather you should have feared Me."