On the authority of Abu Sa'id (radhi Allah 'anhu), who said that the Messenger of Allah (salallahu 'alaihi wassalam) said: "Let not any one of you belittle himself. They said: O Messenger of Allah, how can any one of us belittle himself? He said: He finds a matter concerning Allah about which he should say something, and he does not say [it], so Allah (mighty and sublime be He) says to him on the Day of Resurrection: What prevented you from saying something about such-and-such and such-and-such? He say: [It was] out of fear of people. Then He says: Rather it is I whom you should more properly fear."[Hadith from al-Tirmidhi, Number 5083, Narrated Abu Dharr, related by Ibn Majah with a sound chain of authorities].