Don't spray directly in the face have hose on low and go up behind eye or between ears and if they move go with them don't back down until they relax or lick took a year with my Arabian but it payed off
Work up to hosing his face. Hose his neck and praise him when he doesn't react and slowly work up his neck, ensuring you keep praising him. When you get to his face, don't hose it straight away, work up his neck to it and keep praising him while you hose it.
Maybe try taking a bucket with sweet feed (pellets mixed with molasses) and give it to him when you hose his face. He will associate that with rewards and will eventually get used to it.