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The man does not have to offer expiation if intercourse happens out of forgetfulness. This is the opinion of the majority from the Hanafiโs, Maalikiโs, Shafaโis, and a report by Imam Ahmad that was chosen by Shaykh al-Islam ibn Taymiyyah, ibn al-Qayyim, al-Sanโani, and al-Showkani.
As for the requirement of making up the day, there is a difference of opinion on the matter:
The majority of the scholars state that he does not have to make up that day. [Hanafiโs, Shafaโis, and a report by Imam Ahmad that was chosen by Shaykh al-Islam ibn Taymiyyah, ibn al-Qayyim, al-Sanโani, and al-Showkani]
Maalikiโs and Hanbaliโs state that he must make up the day, and that is the most cautious opinion. And Allah the Exalted knows best.