In one of his articles¹, Mr. Jochen Katz has pointed out a contradiction in two verses of the Qur’an. He writes :

Those who slander chaste women are cursed forever² [in this life and the Hereafter] according to 24:23. However, according to another verse of the Qur’an, the slanderer may be forgiven … But 24:5 says that they can be forgiven if they repent after they have been beaten with 80 stripes. Since it says to let them come back into full rights as members of society, restoring their right to testify, BECAUSE Allah is (also) oft-forgiving, most Merciful.

    He continues:

The earthly forgiveness would not have any foundation or counterpart if Allah would not extend forgiveness as well. That is the very basis on which He commands earthly forgiveness.

    In this article, we shall consider the criticism of Mr Katz in the light of the referred verses of the Qur’an. The two verses of the Qur’an, pertinent to Mr. Katz’s criticism are 24: 23 and 24: 4 - 5. The first one reads as follows:

Those who slander against chaste, innocent, believing women shall indeed be cursed in this world as well as in the Hereafter. For them shall be a grievous punishment. (24:23)

    The second one says:

Those who slander against chaste women and then do not produce four eye witnesses, shall be awarded with eighty lashes and their testimony shall never be accepted after this. These are the [true] transgressors, except those who [sincerely] repent after this and correct themselves, for, then, God is indeed forgiving, merciful. (24:4-5)

    I really do not understand what the contradiction is in these two verses. The first one (24:23) tells us that slanderers shall face a grievous punishment in this world as well as in the Hereafter, while the second set of verses (24:4-5) explains the punishment that shall be administered on such slanderers in this world (eighty lashes and disqualification from testifying forever) and in the Hereafter (being placed in the category of transgressors). However, the second set of verses (24:4-5) has also mentioned the obvious exception that if such people repent and correct their behaviour, they shall then not be dealt with as transgressors (in the Hereafter).
    I have already explained in one of my earlier responses to one of Mr. Katz’s criticisms titled: ‘Does Allah forgive Shirk?’ that according to the Qur’an, true and sincere repentance and subsequent correction of one’s behaviour not only does away with the punishment of all sins in the Hereafter -- however grave the sins may be -- but also converts the sins into good deeds (25:68-71). Therefore, even if the Qur’an has not mentioned (in 24:5) that the only exception would be those who repent and correct their behaviour, it would still have been understood (by a student of the Qur’an) to be an exception, in the light of the other verses of the Qur’an.
Keeping the above explanation in perspective, it should be clear that even though 24:23 has not mentioned the exception clause, yet it is clear that even there the punishment mentioned is for such slanderers who do not repent on their past doings and do not correct their behaviour. The verse, should more accurately be understood as follows:

Those who slander against chaste, innocent, believing women [and then neither repent for their slander nor correct their behaviour], shall indeed be cursed in this world as well as the Hereafter. For them shall be a grievous punishment.

    Stating it even more generally, all the punishments of sins mentioned in the Qur’an entail the obvious exception of repentance and correction during the life of this world, in the light of the Qur’an itself.
    The above explanation should suffice as a response to the criticism of Mr. Katz. However, I would like to clarify here that 24:5 is construed by some of the interpreters of the Qur’an to imply an exception to the worldly punishment mentioned in the previous verse³. In my opinion, this is not correct. Earthly punishments, mentioned in the Qur’an are generally not accepted with repentance, due to the simple reason that the sincerity and the truthfulness of repentance is a matter of the heart, not known to man. Thus, a murderer or a fornicator or a thief may repent for his deeds and promise to correct his behaviour after being caught by the authorities, yet the prescribed punishment will be administered on him and he will deserve no leniency, merely on the grounds of repentance and resolve to correction. However, his sincere repentance and true resolve to correction will save him from the grievous punishment for his sins in the Hereafter.
    Thus, the earthly punishment mentioned in 23:4 (eighty lashes and disqualification from testifying forever) will be administered even in the face of sincere repentance and resolve to correction. However, true repentance and correction will qualify the sinner for the forgiveness and the mercy of the Lord, in the Hereafter.
    In view of the above explanation, 23:4-5 should be understood as:

Those who slander against chaste women and then do not produce four eye witnesses, shall be awarded with eighty lashes and their testimony shall never be accepted after this. These are the [true] transgressors [and shall, therefore, be punished by God as transgressors deserve to be punished,] except those who [sincerely] repent after this and correct themselves, for then God is indeed forgiving, merciful.