I was curious on what the rules were for doing art?

I was thinking of doing custom lion lineart coloring from off of Deviantart and was wondering if that was acceptable? I'd be using someone else's lineart or paying for it, and then color it in myself, as well as giving the credits to the person who orders one to put on their profile since it would be for profile pictures.

If that isn't ok, please let me know! Thank you! <3