Endomorphism Ring of Abelian Group is Ring with Unity

Theorem
Let $\left({G, +}\right)$ be an abelian group.

Let $\left({\operatorname {End} \left({G}\right), +, \circ}\right)$ be its endomorphism ring.

Then $\left({\operatorname {End} \left({G}\right), +, \circ}\right)$ is a ring with unity $I_G$, where $I_G$ is the identity mapping on $G$.