Gemara Shabbos says that originally one was allowed to bathe on Shabbos in pre-heated bath-houses. However, (in short) due to the fact that the bath-house directors would violate Shabbos (by heating ...
The Shulchan Aruch (Orach Chaim 260) writes that there is a mitzvah to wash one's body on Erev Shabbos with hot water, as seen in Tractate Shabbos 25b. The Biur Halacha writes that one can argue about ...
If one looks into the Tur Beis Yosef (and Shulchan Aruch) in Orach Chaim Siman 326 you will find the halachos of bathing on Shabbos. The Beis Yosef there points to the gemorah where it outlines the ...