365.Umar bin Abdul Aziz wrote to Abu Bakr bin Hazm, "look for the knowledge of Hadith and get it written, as I am afraid that religious knowledge will vanish and the religious learned men will pass away (die). Do not accept anything save the Hadiths of the Prophet may the blessings and peace of Allah be upon him). Circulate knowledge and teach the ignorant, for knowledge does not vanish except when it is kept secretly (to oneself).
(Sahih Al-Bukhari Vol 1).
(Dr. Muhammad Muhsin Khan et.al.).