Sahih Bukhari Volume 8, Book 73, Hadith Number 208.

Narated By Jabir bin ‘Abdullah : A man among us begot a boy whom he named Al-Qasim. The people said (to him), “We will not call you Abul-l-Qasim, nor will we please you by calling you so.” The man came to the Prophet and mentioned that to him. The Prophet said to him, “Name your son ‘Abdur-Rahman.”