Reference for Shevuot 91:15
אלמא עביד איניש דגזים ולא עביד הכא נמי דגזים ולא עביד אימא ומשכנו וליחזי מאי משכנו אמר רבה בר בר חנה אמר רבי יוחנן בטוענו כלים הניטלין תחת כנפיו
an enactment was instituted in favour of the hired labourer,<span class="x" onmousemove="('comment',' That the oath be removed from the employer and given to the labourer, who takes the oath, and receives his claim.');"><sup>29</sup></span> but in [an oath imposed by] the Rabbis,<span class="x" onmousemove="('comment',' Where the employer denies the whole; and there is only the Rabbinic oath of equity.');"><sup>30</sup></span> which is itself an enactment - we do not impose one enactment upon another enactment.<span class="x" onmousemove="('comment',' By removing this oath from the employer and giving it to the labourer.');"><sup>31</sup></span>