(Devarim 23:15) "For the L-rd your G-d walks in the midst of your camp … And let your camp be holy": Make it holy — whence it was ruled: One should not recite the Shema near the washers' dippings, nor should he enter a bathhouse or a tannery with scrolls or tefillin in his hand.
God Walks in the Midst of Your Camp, So Keep It Holy
Sifrei Devarim 258:1