Sahih Al Bukhari – Book of Good Manners And Form (Al-Adab)

Volumn 008, Book 073, Hadith Number 209.
—————————————–
Narated By Al-Musaiyab RA: That his father (Hazn bin Wahb) went to the Prophet PBUH and the Prophet PBUH asked (him), "What is your name?" He replied, "My name is Hazn." The Prophet PBUH said, "You are Sahl." Hazn said, "I will not change the name with which my father has named me." Ibn Al-Musaiyab added: We have had roughness (in character) ever since.