It was narrated that Abu Sa'eed Al-Khudri said:
"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." (JA)
English reference (JA): Vol. 1, Book 1, Hadith 265 (JA)
Arabic reference (JA): Book 1, Hadith 277 (JA)