$$\newcommand{\brak}[1]{\left\langle #1 \right\rangle}$$
I'm trying to study Path Integral approach to Quantum Mechanics on my own, during the readings, I came across one part that I'm not certain how it was exactly derived, could use any possible hint and advice.
Consider the quantity: $\brak{x'\mid\exp(-iH\epsilon /\hslash)\mid x} =\int dp \brak{x'|p}\brak{p|\exp(-iH\epsilon/\hslash)|x}$
if we stick to the simple case $H =\frac{\hat{p}^2}{2m} + V(\hat{x})$, then should be able to reach
$\brak{p\mid\exp\left(-i\frac{\epsilon}{\hslash}\left[\frac{\hat{p}^2}{2m} + V(\hat{x})\right]\right)| x} = \exp\left(-i\frac{\epsilon}{\hslash}\left[\frac{\hat{p}^2}{2m} + V(\hat{x})\right]\right)\brak{p|x} + O(\epsilon^2)$
I'm wondering how this $O(\epsilon^2)$ term was obtained? If possible, can someone show me the derivation?