The problem of the one who memorizes Qur’aan and comments on it
Question

                Which books of Tafseer do you advise me to read? And with regard to memorizing Qur’aan – if a person memorizes Qur’aan then forgets it, is there any warning of punishment in this case? How should one retain what one has memorized?
Praise be to Allah. 
          Shaykh Muhammad ibn Saalih al-‘Uthaymeen 
          (may Allaah have mercy on him) was asked this question and he replied 
          as follows: 
 
          The sciences of the Qur’aan vary. Every 
          mufassir who comments on the Qur’aan focuses on one aspect of these 
          sciences. It is impossible for one tafseer to encompass all aspects 
          of the Qur’aan. 
 
          Among the scholars are those who focus 
          on the theoretical aspects of tafseer, like al-Zammakhshaari and others. 
          But I think that he should think of the meaning of the aayah himself 
          first – i.e., he should think of the meaning of the aayah – then he 
          should check what the scholars said concerning it, because this will 
          help him to be strong in Tafseer and not dependent on others. From the 
          time when the Messenger 
          
          (peace and blessings of Allaah be upon him) was sent until the present, 
          the word of Allaah has always been “In the plain Arabic language” (cf. 
          al-Shu’araa 26:195 – interpretation of the meaning). 
 
          It is necessary to refer to the tafseer 
          of the Sahaabah, because they had the greatest understanding of its 
          meanings; then to the books of the mufassireen among the Taabi’een. 
          But despite that no one can ever encompass all the meanings of the words 
          of Allaah. 
 
          What I think is the best way is for a 
          person to think of what an aayah means, then to refer to the words of 
          the scholars. If he finds that his view is the same, that will help 
          him to become good in tafseer and make it easy for him. If he finds 
          that his view is different, then he should follow that which is correct. 
 
          With regard to memorizing the Qur’aan, 
          the way in which it is memorized varies from one person to another. 
          Some people memorize Qur’aan aayah by aayah, i.e., they memorize one 
          aayah, reading it two or three times, then they work at it until they 
          have memorized it, then they memorize the following aayah, and so on 
          until they have completed one-eighth or one-quarter of the juz’ and 
          so on. Other people read the whole one-eighth of a juz’  and repeat 
          it until they have memorized it. In such matters we cannot lay down 
          a general rule, so we tell people, use whatever method suits you to 
          memorize Qur’aan. 
 
          But it is important that you should know 
          what you have memorized when you want to go back to it. The best way 
          that I have seen is that if a person memorizes something on one day, 
          he should read it again early the following morning. This is a great 
          help in remembering what he memorized on the previous day. This is something 
          that I have done myself and it was a great help in memorizing properly. 
 
          With regard to the warning against one 
          who forgets, Imaam Ahmad said, “How severe the warning is,” i.e., against 
          one who memorizes an aayah then forgets it. What is meant here is the 
          one who neglects it until he forgets it. But if a person forgets it 
          because of some natural reason or because of duties which he got involved 
          in, which kept him away from revising what he mad memorized, in this 
          case he is not guilty of sin. “Allaah burdens not a person beyond 
          his scope” [al-Baqarah 2:286 – interpretation of the meaning]. 
 
          It was reported that the Prophet 
          
          (peace and blessings of Allaah be upon him) led his companions in prayer, 
          and he forgot an aayah. One of his companions reminded him of it after 
          the prayer. He said, “Why did you not remind me of it sooner?” But the 
          one who is negligent concerning that or who turns away from it is undoubtedly 
          a loser and deserves to be guilty of sin But the one who forgets it 
          because he became involved in duties which Allaah has enjoined upon 
          him, or who forgot it for some natural reason, is not guilty of anything.