associativity of the composition of morphisms

Let \(\mathcal{C}\) be a category and \(f \in \mathrm{Hom}_{\mathcal{C}}(A,B), g \in \mathrm{Hom}_{\mathcal{C}}(B,C), h \in \mathrm{Hom}_{\mathcal{C}}(C,D)\) for objects \(A,B,C,D \in \mathrm{Ob}(\mathcal{C})\) Then the composition of morphisms is associative, i.e.

\begin{align*} h \circ (g \circ f) =& (h \circ g) \circ f \end{align*}