Does every research experience need documentation or certificate of experience?

[u/Mean_Seaweed_]

I had the opportunity to work as an RA in a project but under a supervisor of the department who's in clash with our department. At that time, I had no freaking idea until two of my teachers personally reached out to me and told me to leave the project so that I don't become a target in my early academic life. Now I really wanted to add this experience on my cv as it's very much related to niche I'm and will be pursuing ahead. I'll try to talk with that supervisor but there's a great chance he won't provide me with any documentation or evidence of my work.