Source for p-adic cyclotomic character

Question

I am looking for some book or paper where the p-adic cyclotomic character $\chi _{p}:G\rightarrow {\mathbf {Z}}_{p}^{\times }$ is defined (as in the wikipedia article https://en.wikipedia.org/wiki/Cyclotomic_character). I want to use it as a reference in my thesis and therefore can not use the wikipedia page itself.