Praise be to Allaah.
We praise Allaah for having enabled them to repent, and we ask Him to reward them and make them steadfast. Undoubtedly the immoral actions that they committed are causes of Allaah’s punishment in this world and in the Hereafter, but there is the hope that sincere repentance from this action, regret for what was done, resolve not to do it again, and weeping for having sinned against Allaah and violated the sanctity of the Muslims will all be good for this repentant person and will be the cause of his or her bad deeds being turned to good deeds.
This sister’s repentance should not lead her to despair of the mercy of Allaah, for the Shaytaan will exploit this and will prevent her from repenting and doing good deeds.
It is good that she regrets what she did and weeps and repents and prays for forgiveness, out of recognition of the seriousness of the sin that she and her husband committed. But it is not good for her to despair of the mercy of Allaah and think badly of Him, may He be exalted.
Our Lord has told us that He forgives all sins, no matter how great they are or how many, if we repent to Him, and He has forbidden us to despair of His mercy, as He says (interpretation of the meaning):
“Say: O ‘Ibaadi (My slaves) who have transgressed against themselves (by committing evil deeds and sins)! Despair not of the Mercy of Allaah, verily, Allaah forgives all sins. Truly, He is Oft‑Forgiving, Most Merciful”
And He has told us that He will turn evil deeds to good deeds for the one who is sincere in his repentance, even if he has committed shirk and murder and zina, which are the gravest of sins. Allaah says (interpretation of the meaning):
“And those who invoke not any other ilaah (god) along with Allaah, nor kill such person as Allaah has forbidden, except for just cause, nor commit illegal sexual intercourse -- and whoever does this shall receive the punishment.
69. The torment will be doubled to him on the Day of Resurrection, and he will abide therein in disgrace;
70. Except those who repent and believe (in Islamic Monotheism), and do righteous deeds; for those, Allaah will change their sins into good deeds, and Allaah is Oft‑Forgiving, Most Merciful”
Our Prophet (peace and blessings of Allaah be upon him) told us that Allaah rejoices over the repentance of His slave and that the one who repents from sin is like one who did not sin.
Hence we can see that it is wrong to say that the one who commits zina will be punished in this world and in the Hereafter even if he repents. The evidence quoted above proves that this idea is false. Rather Allaah encourages His slaves to repent and rewards them for it if they do it; He does not punish them.
So there is no need to fear having children and no need to be anxious.
Ask Allaah for righteous children, and seek the help of your Lord, and do many good deeds. We ask Allaah to help you to do that which pleases Him.
And Allaah knows best.