Sahih al-Bukhari, Hadith 6474 ⓘ
Narrated Sahl bin Sa`d: Allah's Messenger 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 " .
also referenced under: Book 81, Hadith 63 (In-Book) & Volume 8, Book 76, Hadith 481 (USC-MSA)