Reference for Shevuot 91:11
ואלא מאי רבנן ואלא הא דתני רבה בר שמואל קצץ המוציא מחבירו עליו הראיה מני לא רבי יהודה ולא רבנן
I stipulated to pay you only one.'<span class="x" onmousemove="('comment',' Hence, even in a case where the amount stipulated is in dispute. R. Judah states clearly that the labourer takes an oath.');"><sup>19</sup></span> But if he says to him, 'I never hired you at all,' or, if says to him, 'I hired you, and paid you your wages,' then he who desires to exact from his neighbour must bring proof.<span class="x" onmousemove="('comment',' The labourer must bring witnesses, and if not, the employer is exempt, for he denies the whole claim.');"><sup>20</sup></span> To this R'Shisha the son of R'Idi demurred: Well then, [in the case where the dispute is about the amount] stipulated [is this ruling]<span class="x" onmousemove="('comment',' That the labourer takes the oath.');"><sup>21</sup></span>