The Gemara in Shabbos (33b) teaches that when R’ Shimon bar Yochai was hiding in the cave for twelve years, he would sit covered in sand, and didn’t wear clothes. He was scared that his clothes would wear out, and he only put them on when he would daven.
What happened on Shabbos: Did he do the same thing, sit the entire day covered in sand, and when time for davening came he got dressed? Or perhaps on Shabbos he was unable to sit covered in sand, as when going in and out of the sand he would be making a hold in the sand and moving muktzeh, therefore he wore his clothes the entire Shabbos?
The Madanay Asher says that it is logical that on Shabbos he didn’t sit in a pit off sand due to the concern of making holes and covering holes, rather he wore his clothes the entire Shabbos.
The Maharsha explains that the reason R’ Shimon bar Yochai put on clothes for davening was not because of ervah, as he was anyway covered with sand, rather it was due to the halachah of: הכון לקראת א-להיך – “Prepare to meet your G-d” (see Shabbos 10a), a halachah which requires that one dress respectfully when davening. On Shabbos there is an obligation to wear Shabbos clothes, due to the obligation of וכבדתו – “you shall honor it” (see Shabbos 114), consequently, it’s logical that he wore his clothes the entire Shabbos.
