Answer
(Fatwa: 31/31=M)
Adulterer can marry his adulteress provided there is no other relation between them that prevents nikah (like nasab, razaat etc). If an unmarried is involved in adultery a Muslim state can punish him with 100 lashes. The punishment of 80 whips is meant for one who accuses a modest person of adultery. These punishments have been mentioned in the Quran. This penal code can be implemented only under Islamic governments; therefore at other places where there is no Islamic government one should do isteghfar and taubah.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband