What is the ruling on one who performs the obligatory prayers and fasting, but neglects to pay Zakat al-Fitr out of leniency?

Zakat al-Fitr is obligatory upon every Muslim who possesses more than their sustenance and the sustenance of their dependants for the day and night of Eid. Delaying it beyond the day of Eid is Haram by consensus. Whoever has not paid it must pay it for the previous years, along with repentance and seeking forgiveness, because it is a right of the poor and needy and is not forfeited except by its payment. This is what the four schools of thought have agreed upon.