O Hisham, Allah’s saying, ‘Is the reward for good [anything] but good?’ applies to both the believer and the disbeliever, and to the righteous and the corrupt. The one to whom a favor has been done must requite the favor, and the requital is not realized through doing exactly the same favor that has been done to him, rather it should be with something better, for if he does exactly the same favor that has been done to him, then the good doer has the advantage of initiating the favor.