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

Intercourse during the day in Ramadaan 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 Allaah
be pleased with him) who said: a man came to the Prophet (peace and
blessings of Allaah be upon him) and said, “O Messenger of Allaah, 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 Allaah (peace and
blessings of Allaah 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 –
Allaah forbid. 

The one who does that violates two sacred things: the
sanctity of the month and the sanctity of a forbidden relationship. And
Allaah is the One Whose help we seek. 

This young man has to repent mightily to Allaah, 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 Allaah to forgive him and us, and to accept his
repentance and ours. Ameen.