Sahih Bukhari Volume 8, Book 73, Hadith Number 209.

Narated By Al-Musaiyab : That his father (Hazn bin Wahb) went to the Prophet and the Prophet asked (him), “What is your name?” He replied, “My name is Hazn.” The Prophet 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.