Reference for Shabbat 33:3
וא"ר ינאי ומרדע שאמרו אין בעביו טפח ויש בהיקפו טפח וגזרו על היקפו משום עביו
of a handbreadth. And R. Jannai observed: and the ox-goad of which they spoke is not a handbreadth in thickness but in circumference, and they enacted [this law] concerning its circumference on account of its thickness.<span class="x" onmousemove="('comment',' If its thickness is a handbreadth, it induces uncleanness of seven days by Biblical law, and therefore the Sages extended this to the former case too, to prevent confusion. This is one of the eighteen enactments. V. Oh. XVI, 1. ');"><sup>5</sup></span> But according to R. Tarfon who said, 'May I bury my children but this <i>halachah</i> is incorrect!' they are less [than eighteen]? — Said R. Nahman b. Isaac, That the daughters of Cutheans are niddoth from their cradles was also enacted on that same day; and on the other [question]<span class="x" onmousemove="('comment',' Sc. one who places vessels under a spout, v. supra 16b. ');"><sup>6</sup></span>