Language:
كتاب الرقاق
81  
To make the Heart Tender (Ar-Riqaq)
(23)
Chapter: To protect one's tongue
(23)
باب حِفْظِ اللِّسَانِ
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 ‏"‏‏.‏
Reference : Sahih al-Bukhari 6474
In-book reference : Book 81, Hadith 63
USC-MSA web (English) reference : Vol. 8, Book 76, Hadith 481
  (deprecated numbering scheme)