In such cases, according to most scholars and the four imams, that person is to make up that day. However, there is a difference of opinion on this point. Ishaq, Dawud, Ibn Hazm, ‘Ata, ‘Urwah, al-Hassan al-Basri, and Mujahid maintain that such a fast is sound and that the person need not make up the day later. They base their opinion on the fact that Allah says in the Qur’an: “And there is no sin for you in the mistakes you make unintentionally, but what your hearts purpose [that will be a sin for you].”
Section : If one eats, drinks, or has intercourse, thinking that the sun has set or that fajr has not occurred.