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.'" (ES)
English reference (ES): Vol. 1, Book 1, Hadith 58 (ES)
Arabic reference (ES): Book 1, Hadith 61 (ES)