Sahih Bukhari Volume 008, Book 077, Hadith Number 600.
Narated By Abu Said Al-Khudri : That while he was sitting with the Prophet a man from the Ansar came and said, "O Allah's Apostle! We get slave girls from the war captives and we love property; what do you think about coitus interruptus?" Allah's Apostle said, "Do you do that? It is better for you not to do it, for there is no soul which Allah has ordained to come into existence but will be created."