Sahih Bukhari Volume 8, Book 73, Hadith Number 205.

Narated By Jabir : A boy was born for a man among us, and the man named him Al-Qasim. We said to him, “We will not call you Abu-l-Qasim, nor will we respect you for that.” The Prophet was informed about that, and he said, “Name your son ‘Abdur-Rahman.”