Sunan an-Nasa'i 5033
It was narrated from Salim, from his father, that:
The Messenger of Allah [SAW] passed by a man who was censuring his brother about modesty. He said: "Let him be, for modesty is part of faith."
أَخْبَرَنَا هَارُونُ بْنُ عَبْدِ اللَّهِ قَالَ حَدَّثَنَا مَعْنٌ قَالَ حَدَّثَنَا مَالِكٌ ح وَالْحَارِثُ بْنُ مِسْكِينٍ قِرَاءَةً عَلَيْهِ وَأَنَا أَسْمَعُ عَنْ ابْنِ الْقَاسِمِ أَخْبَرَنِي مَالِكٌ وَاللَّفْظُ لَهُ عَنْ ابْنِ شِهَابٍ عَنْ سَالِمٍ عَنْ أَبِيهِ  أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مَرَّ عَلَى رَجُلٍ يَعِظُ أَخَاهُ فِي الْحَيَاءِ فَقَالَ دَعْهُ فَإِنَّ الْحَيَاءَ مِنْ الْإِيمَانِ