Given a function $f○g○h(x)$, where $f,g,h$ are bijective functions and $○$ is used to denote composition of functions . Then prove that $(f○g)○h(x)$

Question

Given a function $f○g○h(x)$, where $f,g,h$ are bijective functions and $○$ is used to denote composition of functions . Then prove that $(f○g)○h(x)=f○(g○h)(x)$. I am not been able to quite solve it .

My approach goes like this :

First of all, we know that if $f(x)$ and $g(x)$ are bijective functions then $f○g(x)$ is also a bijective functions. Now, considering $f○g(x)=\phi(x)$ so, $\phi○h(x)$ is also a bijective one . Now if $g○h(x)=\sigma(x)$ then $f○\sigma(x)$ is a bijective function as well. Now, how to prove that $f○\sigma(x)=\phi○h(x)$?

I can't seem to get it...