Where is the logarithmic derivative at $s=0$ of the L-function of a Dirichlet character computed? Many people cite the Hurwitz formula but I was unable to find a suitable reference.

In this post there is a formula for the logarithmic derivative but no further reference (only the computation of the value $L(0, \chi)$ is discussed). I already know the formula. What I want is a reference in which it is proved.
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carapaceJan 21 '14 at 13:43