He fasted the day of ‘Arafah with the intention of making up a day from Ramadaan

Praise be to Allah.

It is permissible to fast on the day of ‘Arafah to make up for a missed Ramadaan fast, if one intends it to make up that fast. 

And Allaah is the Source of strength. May Allaah send blessings and peace upon our Prophet Muhammad and his family and companions. End quote. 

Standing Committee for Academic Research and Issuing Fatwas