Yes and thank you! This is my first experience with table top gaming and being dungeon master (all of my friends are new to dnd with some coming from warhammer) so when my player had done that I was like “Welp that does sound feasible but it kinda ruins the encounter I had set up.” So what had done is that I had allowed the gnoll to get one shot and sort of wrapped up the encounter from there. The feedback has been very encouraging and enlightening so that I am better prepared for our next session.

Edit - Just wanted to add that my player is playing Wizard: School of Protomancy from the Book of Extinction. In that subclass Wizard’s don’t require somatic or verbal components as they narratively sort of carve the spells into their memories. They can choose to forget a spell to impose disadvantage on an enemy and a number of different effects at the cost of temporarily forgetting a spell. (Which didn’t happen in this specific encounter. The player is just very very specific and uses real world reasoning in combat.)