abstract algebra – Prove that ρ is irreducible when $Mρ(x)=ρ(x)M$

Be ρ: G $rightarrow$ GL(n;$mathbb{C}$) a representation of the finite group G. Prove that ρ is irreducible exactly when each matrix M ∈ Mat(n;$mathbb{C}$) with $Mρ(x)=ρ(x)M$, for each $x ∈ G$, of the shape $λE$ for a scalar of the λ ∈ $mathbb{C}$.

Can anyone give me some help?