Sahih Bukhari Volume 003, Book 031, Hadith Number 129.

Narated By 'Alqama : While I was walking with 'Abdullah he said, "We were in the company of the Prophet and he said, 'He who can afford to marry should marry, because it will help him refrain from looking at other women, and save his private parts from looking at other women, and save his private parts from committing illegal sexual relation; and he who cannot afford to marry is advised to fast, as fasting will diminish his sexual power."