Lie-Trotter Theorem proof

Question

Does anyone know how to prove Lie-Trotter theorem: $e^{-iA}e^{-iB}=e^{-i(A+B)}+\mathcal{O}(\delta^{2})$ whereby, $||A||, ||B||<\delta$ and $\mathcal{O}(\delta^{2})$ is shorthand for some arbitrary operator, $E$, where $||E||<\delta^{2}$.