Narrated Sahl bin Sa'd: Allah's Apostle said, "Whoever can guarantee (the chastity of) what is between his two jaw-bones and what is between his two legs (i.e. his tongue and his private parts), I guarantee Paradise for him."
— Sahih Bukhari, Volume 8, Book 76: To make the Heart Tender (Ar-Riqaq), Hadith #481
