Sahih Bukhari Volume 008, Book 076, Hadith Number 481.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 76. To Make the Heart Tender (Ar-Riqaq)
Narated By 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."