All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
Muslim scholars agree with consensus that it is prohibited to abort the fetus after the soul has been breathed into it when completing four months. Ibn Juzayy said: “When the womb receives the sperm, it is prohibited to endanger it. It is worse (to do so) when it (the fetus) has been formed; and it is even worse when the soul has been breathed into it, for that is considered as killing a soul, according to scholarly consensus.”
Accordingly, it is not permissible to abort the fetus after 120 days of the pregnancy, even if the pregnancy is due to Zina (i.e. fornication) or rape, as this does not make abortion permissible. For more benefit, kindly refer to Fatwa 2208.
Aborting the fetus in this case is a form of killing the protected soul (whose killing is Islamically prohibited), then Diyah (blood money) will be obligatory (upon the killer) which is freeing a male or female slave. If that is not available, then its value has to be what equals five camels. Also, some scholars view that the expiation of killing has to be paid for it.
For more benefit on the punishment of that brother who committed incest, please refer to Fataawa 86063 and 84136.
Allaah Knows best.