Commentary for Berakhot 40:13

אי אמרת בשלמא דאורייתא אתי דאורייתא ומפיק דאורייתא אלא אי אמרת דרבנן אתי דרבנן ומפיק דאורייתא

This is quite right if thou sayest that it is from the Torah; then one who is enjoined by the Torah [to keep the observance] comes and exempts one [whose observance is likewise commanded] by the Torah. But if thou sayest it is from the Rabbis, then one who is enjoined by the Rabbis [to keep the observance] comes and exempts one [whose observance is commanded] by the Torah !

Abraham Cohen Footnotes to the English Translation of Masechet Berakhot