Sahih al-Bukhari 120
Sahih al-Bukhari · Book 3: Knowledge · (What is said regarding) the memorization of (religious) knowledge
Narrated Abu Huraira:
حَدَّثَنَا إِسْمَاعِيلُ ، قَالَ حَدَّثَنِي أَخِي ، عَنِ ابْنِ أَبِي ذِئْبٍ ، عَنْ سَعِيدٍ الْمَقْبُرِيِّ ، عَنْ أَبِي هُرَيْرَةَ ، قَالَ حَفِظْتُ مِنْ رَسُولِ اللَّهِ صلى الله عليه وسلم وِعَاءَيْنِ، فَأَمَّا أَحَدُهُمَا فَبَثَثْتُهُ، وَأَمَّا الآخَرُ فَلَوْ بَثَثْتُهُ قُطِعَ هَذَا الْبُلْعُومُ.
I have memorized two kinds of knowledge from Allah's Messenger (ﷺ) . I have propagated one of them to you and if I propagated the second, then my pharynx (throat) would be cut (i.e. killed).