What is the ruling on one who forgot to pay Zakat al-Fitr and remembered it after the Eid prayer?

There is no sin upon one who forgot to pay Zakat al-Fitr on time; rather, he must pay it whenever he remembers. Sheikh Abdul Aziz bin Baz, may Allah have mercy on him, was asked about this and he replied that paying it after the prayer is sufficient, because the delay was not intentional but due to forgetfulness, and Allah the Almighty does not hold one accountable for forgetfulness. Sheikh Ibn Uthaymeen, may Allah have mercy on him, added that performing it after the prayer is acceptable in cases of excuse, such as forgetfulness or inability to pay it on time, and by analogy with the prayer that is offered when a sleeping person or a forgetful person remembers it.