Sunan Abi Dawud, Hadith 4777

`Abd Allah b. ‘Umar said: The Prophet passed by a man of the Ansar when he was giving his brother a warning against modesty. The Apostle of Allah said : Leave him alone, for modesty is a part of faith.

حَدَّثَنَا الْقَعْنَبِيُّ، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ سَالِمِ بْنِ عَبْدِ اللَّهِ، عَنِ ابْنِ عُمَرَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم مَرَّ عَلَى رَجُلٍ مِنَ الأَنْصَارِ وَهُوَ يَعِظُ أَخَاهُ فِي الْحَيَاءِ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ دَعْهُ فَإِنَّ الْحَيَاءَ مِنَ الإِيمَانِ ‏" ‏ ‏.‏

sunnah.com

also referenced under: Hadith 4795 (DarusSalam)