Medieval Christian adoption of Jewish Sabbath

Ilana Ben-Ezra's picture

Dear fellow medievalists, 


I am wondering if anybody has any information - primary or secondary sources are both welcomed - on Christian observance of the Sabbath on Saturday, instead of Sunday.  I am in the process of writing about Raymond de Penaforte's (d. 1275) Summa de Paenitentia and he includes an interesting case warning Christians against observing the Jewish sabbath.  This can obviously be a purely polemical reference and spritual admonishment, but I am wondering if there is any possibility that he was responding to actual Christian practices, since his work was a penitential handbook meant to guide the laity.  If anybody has any information on this topic, it would be much appreciated. 



Ilana Ben-Ezra