Reference for Bava Metzia 143:3
תנו רבנן ישראל שלוה מעות מן הנכרי ברבית וזקפן עליו במלוה ונתגייר אם קודם שנתגייר זקפן עליו במלוה גובה את הקרן וגובה את הרבית ואם לאחר שנתגייר זקפן עליו במלוה גובה את הקרן ואינו גובה את הרבית
But the analogy is false; an Israelite [minor] comes [eventually] within the principle of agency, but a heathen never does.<span class="x" onmousemove="('comment',' For to take possession on another man's behalf is akin to becoming his agent. Thus the Rabbis conferred upon a minor the privilege of being so benefited, because he is potentially an agent or a principal, but a heathen is not even potentially so. [Levinthal, I.H., JQR, (N.S.) XIII, p. 150, suggests the principal reason swaying the Rabbis in their decision barring the heathen from acting as agent to have been the fact that the agent in Jewish law is frequently compelled to take an oath, and the oath being considered a most sacred role in the life of the people there was no desire to force a heathen to comply with the strictness of that act.] ');"><sup>3</sup></span>