Reference for Yoma 60:9

אלא אידי ואידי דלא אסח דעתיה ולא קשיא הא דטביל על דעת ביאת מקדש הא דלא טביל על דעת ביאת מקדש ואב"א תני לא מצורעין אמרו אלא כל אדם

But, if he did not immerse himself, he must await the setting of the sun? - Rather: In both cases he is presumed to have immersed himself, but in the one case he is presumed to have ceased to have his mind [on the necessity of preventing defilement],<span class="x" onmousemove="('comment',' By consistent guarding of his body against touch by agents of ritual uncleanness.');">⁹</span> in the other he is presumed to have had his mind thereon all the time.

Jastrow