Allah will accept whatever righteous deeds from one who commits Zina, such as praying, fasting, giving charity etc., and He will also accept his sincere repentance.

The one who committed Zina (fornication or adultery) during the day in Ramadan has to, along with repenting, make up that day’s fast and offer the severe expiation, which is to free a slave; if she cannot do that, then she must fast for two consecutive months; and if she cannot do that, she must feed sixty poor persons.