What is the ruling on someone who broke their fast in Ramadan out of forgetfulness, then remembered, but did not abstain for the rest of the day due to their ignorance of the obligation to do so in this situation?

Scholars have differed concerning the invalidation of the fast by breaking it out of forgetfulness. The preponderant opinion is that it does not invalidate the fast, and one must complete it. Expiation (kaffarah) is only obligatory for sexual intercourse according to the majority of scholars. However, the Malikis made it obligatory for every intentional breaking of the fast in Ramadan, provided that the sanctity of the month is violated. So, whoever breaks their fast out of forgetfulness and then remembers but does not abstain due to ignorance, must only make up that day.