Is it permissible to pay Zakat al-Fitr after forgetting to give it out due to travel?

Whoever intentionally delays paying Zakat al-Fitr, while remembering it, has committed a sin. They must repent and make it up (qada'), because it is an act of worship that does not lapse with the passage of time, just like prayer (salat). As for one who forgot to pay it on time, there is no sin upon them, but they must make it up (qada').