Sahih al-Bukhari 6474
Narrated Sahl bin Sa`d:
Allah's Messenger (ﷺ) 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."
حَدَّثَنَا مُحَمَّدُ بْنُ أَبِي بَكْرٍ الْمُقَدَّمِيُّ، حَدَّثَنَا عُمَرُ بْنُ عَلِيٍّ، سَمِعَ أَبَا حَازِمٍ، عَنْ سَهْلِ بْنِ سَعْدٍ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ ‏
"‏ مَنْ يَضْمَنْ لِي مَا بَيْنَ لَحْيَيْهِ وَمَا بَيْنَ رِجْلَيْهِ أَضْمَنْ لَهُ الْجَنَّةَ ‏"‏‏.‏