Hadith 22, 40 Hadith Qudsi
On the authority of Abu Sa'id (may Allah be pleased with him), who said that the Messenger of Allah (ﷺ) 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.

It was related by Ibn Majah with a sound chain of authorities.
عَنْ أَبِي سَعِيدٍ رَضِيَ اللَّهُ عَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: 

" لَا يَحْقِرْ أَحَدُكُمْ نَفْسَهُ، قَالُوا: يَا رَسُولَ اللَّهِ كَيْفَ يَحْقِرُ أَحَدُنَا نَفْسَهُ؟ قَالَ: يَرَى أَمْرَ الِلَّهِ عَلَيْهِ فِيهِ مَقَالٌ، ثُمَّ لَا يَقُولُ فِيهِ، فَيَقُولُ اللَّهُ عَزَّ وَجَلَّ لَهُ يَوْمَ الْقِيَامَةِ: مَا مَنَعَكَ أَنْ تَقُولَ فِي كَذَا وَكَذَا؟ فَيَقُولُ: خَشْيَةُ النَّاسِ، فَيَقُولُ: فَإِيَّايَ كُنْتَ أَحَقَّ أَنْ تَخْشَى" 
رواه ابن ماجه بسند صحيح