Mukhtasar Bukhari (Abridged) 927 — An unmarried person fearing sin

Narrated Abdullah bin Mas'ud (may Allah be pleased with him): We were with the Prophet (peace and blessings of Allah be upon him) when he said: "Whoever among you is able to marry, should marry, for it helps him lower his gaze and guard his private parts (from unlawful acts). And whoever is not able to marry, should fast, for fasting diminishes his sexual power." (These fasts are not obligatory, but recommended, and the hadith emphasizes this recommendation.)