The Prophet said: "There is no man who memorizes knowledge then conceals it, but he will be brought forth on the Day of Resurrection bridled with reins of fire." (Hasan) Another chain with similar wording.  

عَنِ النَّبِيِّ ﷺ قَالَ مَا مِنْ رَجُلٍ يَحْفَظُ عِلْمًا فَيَكْتُمُهُ إِلاَّ أُتِيَ بِهِ يَوْمَ الْقِيَامَةِ مُلْجَمًا بِلِجَامٍ مِنَ النَّارِ قَالَ أَبُو الْحَسَنِ أَىِ الْقَطَّانُ وَحَدَّثَنَا أَبُو حَاتِمٍ حَدَّثَنَا أَبُو الْوَلِيدِ حَدَّثَنَا عِمَارَةُ بْنُ زَاذَانَ فَذَكَرَ نَحْوَهُ قَالَ أَبُو الْحَسَنِ أَيْضًا وَحَدَّثَنَا إِبْرَاهِيمُ بْنُ نَصْرٍ قَالَ حَدَّثَنَا أَبُو نُعَيْمٍ قَالَ حَدَّثَنَا عِمَارَةُ بْنُ زَاذَانَ فَذَكَرَ نَحْوَهُ  

"By Allah, were it not for two Verses in the Book of Allah, I would never have narrated anything from him, meaning from the Prophet, were it not for the Words of Allah: Verily, those who conceal what Allah has sent down of the Book, and purchase a small gain therewith (of worldly things), they eat into their bellies nothing but fire. Allah will not speak to them on the Day of Resurrection, nor purify them, and theirs will be a painful torment. Those are they who have purchased error at the price of guidance, and torment at the price of forgiveness. So how bold they are (for evil deeds which will push them) to the Fire.'"  

أَنَّهُ سَمِعَ أَبَا هُرَيْرَةَ يَقُولُ وَاللَّهِ لَوْلاَ آيَتَانِ فِي كِتَابِ اللَّهِ تَعَالَى مَا حَدَّثْتُ عَنْهُ يَعْنِي عَنِ النَّبِيِّ ﷺ شَيْئًا أَبَدًا لَوْلاَ قَوْلُ اللَّهِ {إِنَّ الَّذِينَ يَكْتُمُونَ مَا أَنْزَلَ اللَّهُ مِنَ الْكِتَابِ} إِلَى آخِرِ الآيَتَيْنِ  

"The Messenger of Allah said: 'When the last people of this Ummah curse the first, (at that time) whoever conceals a Hadith will be concealing what Allah has revealed.'" (Maudu')  

قَالَ رَسُولُ اللَّهِ ﷺ إِذَا لَعَنَ آخِرُ هَذِهِ الأُمَّةِ أَوَّلَهَا فَمَنْ كَتَمَ حَدِيثًا فَقَدْ كَتَمَ مَا أَنْزَلَ اللَّهُ  

'I heard Anas bin Malik say: "I heard the Messenger of Allah say: "Whoever is asked about knowledge and conceals it, it will be bridled on the Day of Resurrection with reins of fire.'"  

سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ مَنْ سُئِلَ عَنْ عِلْمٍ فَكَتَمَهُ أُلْجِمَ يَوْمَ الْقِيَامَةِ بِلِجَامٍ مِنْ نَارٍ  

"The Messenger of Allah said: 'Whoever conceals knowledge which Allah has made beneficial for mankind's affairs of religion, Allah will bridle him with reins of fire on the Day of Resurrection."  

قَالَ رَسُولُ اللَّهِ ﷺ مَنْ كَتَمَ عِلْمًا مِمَّا يَنْفَعُ اللَّهُ بِهِ فِي أَمْرِ النَّاسِ فِي الدِّينِ أَلْجَمَهُ اللَّهُ يَوْمَ الْقِيَامَةِ بِلِجَامٍ مِنَ النَّارِ  

"The Messenger of Allah said: 'Whoever is asked about knowledge that he has and he conceals it, will be bridled on the Day of Resurrection with reins of fire.'"  

قَالَ رَسُولُ اللَّهِ ﷺ مَنْ سُئِلَ عَنْ عِلْمٍ يَعْلَمُهُ فَكَتَمَهُ أُلْجِمَ يَوْمَ الْقِيَامَةِ بِلِجَامٍ مِنْ نَارٍ