Reference for Shabbat 254:10
הלך רבי יהושע ותלמידיו כיון שהגיע לפתח ביתה חלץ תפיליו ברחוק ארבע אמות ונכנס ונעל הדלת בפניהן אחר שיצא ירד וטבל ושנה לתלמידיו
at a distance of four cubits, entered, and shut the door in front of them. After he came out he descended, had a ritual bath, and learnt with his disciples. Said he to them, 'When I removed my tefillin, of what did you suspect me?' 'We thought, our Master reasons, "Let not sacred words enter a place of uncleanness".' 'When I shut [the door], of what did you suspect me?' 'We thought, perhaps he has [to discuss] an affair of State with her.' 'When I descended and had a ritual bath, of what did you suspect me?' 'We thought, perhaps some spittle spurted from her mouth upon the Rabbi's garments.'<span class="x" onmousemove="('comment',' Which by rabbinical law affects levitical purity; cf. supra 15b, 17b. ');"><sup>8</sup></span>