Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
Answering your question, the Fatwa Center at Islam Q and A, states:
We read in al-Jawharah al-Nayyirah (1/138), which is a Hanafi book:
And we read in Hashiyat al-Dusuqi (1/523), which is a Maaliki book:
“If a person has intercourse at night and his semen is emitted after dawn, it seems that he does not have to do anything, as is also the case for one who puts on kohl at night then it reaches his throat during the day.”
Al-Nawawi, whose madhhab was Shafa`i, said in al-Majmu` (6/348):
If a person has intercourse before dawn then he withdraws when dawn comes or straight after it comes, then ejaculates, that does not invalidate his fast, because it came as the result of permissible intimacy, so he does not have to do anything. The same applies if a man’s hand is cut off in a case of hadd punishment and he dies as a result (i.e., no one is responsible for his death).
If a person has intercourse then does ghusl, then some semen comes out of him after doing ghusl, he does not have to do ghusl again, because the reason for that is one reason, so there is no need to do two ghusls. Rather he has to do ghusl if he ejaculates again as the result of renewed desire.
Allah Almighty knows best.