Twelve Mil and the Disciple Forbidden to Rule Before His Master

It was taught (in a baraita): A disciple is forbidden to render a halakhic ruling in the presence of his master until he is twelve mil distant from him, corresponding to the camp of Israel. This is what is written (in Numbers 33:49): "And they encamped by the Jordan, from Beth-jeshimoth as far as Abel-shittim." Rabbi Nahum bar Jeremiah was in Hefer. They would ask him, and he would rule; they would ask him, and he would rule. They said to him: But have we not learned thus, Rabbi: "A disciple is forbidden to render a halakhic ruling in the presence of his master until he is twelve mil distant from him, corresponding to the camp of Israel," and behold, Rabbi Mani, [our master], dwells in Sepphoris! He said to them: May it come upon me—had I known, I would not have ruled. From that hour onward he did not rule.