Amir al-Mu'minin fi al-Hadith, Hazrat Imam Bukhari (may Allah have mercy on him) was asked, "What measures should be taken to sharpen the memory?" He replied, "The study of books should be continued constantly." (Memory is strengthened by this.) (Mukhtasar Jami' Bayan al-'Ilm: 398)
Therefore, whoever wants to preserve his knowledge should make arrangements for study and discussion. Without this, his knowledge cannot be preserved, nor can scholarly matters remain present in his mind. If the study of books is abandoned, even the knowledge stored in the mind gradually departs.