Docker images and containers are not the same. See this answer.
docker system prune
tells you:
WARNING! This will remove:
- all stopped containers
- all networks not used by at least one container
- all dangling images
- all dangling build cache
Are you sure you want to continue? [y/N]
So it should be no surprise that it removed your container and possibly also the image it was based on (if no other container was running based on that same image).
I believe it is not possible to recover your image or container, however you can rebuild them. Depending on how the image was obtained you have to run:
docker pull <image> # for an image on dockerhub or other registry
docker build <arguments> # for an image based on a dockerfile
After that you will have your image and you can run a container again with:
docker run <image>