Is it permissible for a father to marry a girl with whom his son committed zina (fornication/adultery) and then refused to marry, in order to cover her?

The most authoritative view is that zina (fornication/adultery) does not prohibit affinity (marriage between in-laws). This is the position of the Maliki and Shafi'i schools of thought. Based on this, it is permissible for the father of the young man to marry the girl with whom his son committed zina, after her repentance and the purification of her womb (i.e., ensuring she is not pregnant). It should be noted that the fornicator is not obligated to marry the person with whom he committed zina, and care must be taken to protect children from corruption.