Calculate product of modified bessel functions of first kind & exponential?

There is a equation which goes like:

\sum_{n=-\infty}^{\infty}I_n(x)e^{-x}=1

where I_n(x) is the Modifed bessel function of first order and e^{-x} is the exponential function.This is a well know relation, which hold good for any value of x.
But, when I tried to do this in Mathematica, it’s not giving any answer.
My code goes like this:

Sum[BesselI[n, x]*E^(-x), {n, -Infinity, Infinity}]

Any help will be really appreciated.

Thanks in advance…