Sunan Ibn Majah, Hadith 58 ⓘ
It was narrated from Salim that his father said: "The Messenger of Allah said heard a man urging his brother to be modest. He said: 'Indeed modesty is a branch of faith.'"
حَدَّثَنَا سَهْلُ بْنُ أَبِي سَهْلٍ، وَمُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ يَزِيدَ، قَالاَ حَدَّثَنَا سُفْيَانُ، عَنِ الزُّهْرِيِّ، عَنْ سَالِمٍ، عَنْ أَبِيهِ، قَالَ سَمِعَ النَّبِيُّ ـ صلى الله عليه وسلم ـ رَجُلاً يَعِظُ أَخَاهُ فِي الْحَيَاءِ فَقَالَ " إِنَّ الْحَيَاءَ شُعْبَةٌ مِنَ الإِيمَانِ " .
also referenced under: Book 1, Hadith 61 (In-Book) & Volume 1, Book 1, Hadith 58 (DarusSalam)