Rashi on Exodus 32:30/רש"י על שמות ל״ב:ל׳

1אכפרה בעד חטאתכם [PERADVENTURE] I SHALL MAKE AN EXPIATION FOR YOUR SIN — i. e. I shall put an effacing and a wiping off and a covering in front of your sin, to serve as a barrier between you and your sin.