How to prove without using advanced theorems that quaternions algebra $H = \genfrac(){}{}{-1,-1}{\mathbb{Z}_p}$, where $p$ is prime that $H \cong\operatorname{Mat}_2({\mathbb{Z}_p})$?

My ideas: I tried to build an explicit isomorphism, but as I think it is only possible when $p = 1 \pmod 4$, and for $p = 1 \pmod 4$ it get it. In my second attempt, I tried to look at them as vector spaces of the same dimension.