The Prophet ﷺ heard a man admonishing his brother about modesty, so he said, "Modesty is a branch of faith."
حدثنا سهل بن أبي سهل ومحمد بن عبد الله بن يزيد قالا حدثنا سفيان عن الزهري
سمع النبي ﷺ رجلا يعظ أخاه في الحياء فقال إن الحياء شعبة من الإيمان
Muslim narrated it, Book of Faith, Chapter on explaining the number of the branches of faith etc., no. 36, from the hadith of Sufyan through this chain. Bukhari also narrated it, Book of Faith, Chapter on modesty being part of faith, no. 24, and others, from the hadith of Malik from Zuhri through this chain.