Do Catholics break the Sabath commandement?

A Protestant Christian approached me and asked me why do catholics break the commandement about the sabath, which should be the 7th day and not the first (or eight day). He claims that this change was decided by St Augustine in the years 400. I did not know what to say to him. I thought the first Christians started celebrating the sabath on Sunday earlier than that as the day of Resurrection. Am I mistaken? Who first decided that the holy day of rest would be Sunday? Are there records, writings by the early Church Fathers discussing this matter?
Thank you.

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