Does a fasting person complete his fast if he eats forgetfully on the Day of Arafah, then remembers after eating?

Voluntary fasting is not valid with an intention made during the day if the fasting person ate or drank before making the intention. This is the view of the majority of scholars, and it is the preponderant opinion.

Al-Khiraqi and Ibn Qudamah stated that among the conditions for the validity of voluntary fasting with an intention made during the day is that the fasting person must not have eaten, drunk, or done anything that breaks the fast before making the intention.

Although there is a weak difference of opinion on the matter, the correct view is that the fast of one who ate or drank before making the intention is not valid. This view is supported by the fact that fasting is only valid if all the conditions of fasting are met from the beginning of the day.