It was narrated from Salim that his father said:
"The Messenger of Allah (ﷺ) said heard a man urging his brother to be modest. He said: 'Indeed modesty is a branch of faith.'" (RU)
English reference (RU): Vol. 1, Book 1, Hadith 58 (RU)
Arabic reference (RU): Book 1, Hadith 61 (RU)