Sahih Bukhari Volume 8, Book 73, Hadith Number 213.

Narated By Said bin Al-Musaiyab : That when his grandfather, Hazn visited the Prophet the Prophet said (to him), “What is your name?” He said, “My name is Hazn.” The Prophet said, ” But you are Sahl.” He said, “I will not change my name with which my father named me.” Ibn Al-Musaiyab added: So we have had roughness (in character) ever since.