How to find the PDF/CDF of the product between an exponential random variable and Erlang random variable ?

Particularly, $Z = XY$ where $X$ follow the Erlang Distribution with parameter $left( {k,{lambda _x}} right)$ and $Y$ follow the Exponential Distribution with parameter ${lambda _y}$.

During my research this derivation become obviously needed but I could not find any way to do it

Please help me

Thank you