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