He committed zina during the day in Ramadan. What should he do?
Question

What should he do? What is the ruling on his fasting? How should he make it up? All of this has to do with a young man who committed zina during the day in Ramadan. What should he do after repenting in the manner advised in books etc?.
Praise be to Allah.Intercourse during the day in Ramadan is one of the most serious of the things that break the fast. Whoever breaks his fast by having intercourse has committed a sin. He has to refrain from eating etc for the rest of that day, and he has to make it up and offer the burdensome expiation. The evidence for that is the hadeeth of Abu Hurayrah (may Allah be pleased with him) who said: a man came to the Prophet (peace and blessings of Allah be upon him) and said, “O Messenger of Allah, I am doomed!” He said: “What is the matter with you?” He said, “I had intercourse with my wife when I was fasting.” The Messenger of Allah (peace and blessings of Allah be upon him) said: “Do you have a slave whom you can set free?” He said, “No.” He said: “Can you fast for two consecutive months?” He said, “No.” He said, “Can you afford to feed sixty poor persons?” He said, “No.” … Narrated by al-Bukhaari, 1936; Muslim, 1111. 
We have already discussed that in detail in questions no. 38023, 22938, 1672 
This applies if he had intercourse with his wife – so how about one who transgressed the sanctity of this month by committing zina – Allah forbid. 
The one who does that violates two sacred things: the sanctity of the month and the sanctity of a forbidden relationship. And Allah is the One Whose help we seek. 
This young man has to repent mightily to Allah, and do good deeds, and do a great deal of righteous deeds, and keep company with righteous people. He should strive to keep himself chaste by getting married if he can afford it, or by fasting, for that will help him to be chaste and to avoid haraam actions. 
What he should do now is to repent from that evil action, make up that day, and offer the burdensome expiation mentioned in the hadeeth quoted above. We ask Allah to forgive him and us, and to accept his repentance and ours. Ameen.