To make the Heart Tender (Ar-Riqaq)

Bukhari :: Book 8 :: Volume 76 :: Hadith 481

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."