Tractate Eduyot - Chapter 3 - Mishnah 7 עדויות פרק ג׳ משנה ז׳

Four cases of doubt Rabbi Joshua pronounces impure, and the Sages pronounce them pure. How is this so? If the impure person stands and the pure person passes by him; or if the pure person stands and the impure person passes by him; or if impurity is in the private domain and something pure is in the public domain; Or if something pure is in the private domain and something impure is in the public domain; If it is doubtful [in all of these case] whether one touched or did not touch the other, or if it is doubtful whether one formed a tent over the other or did not form a tent over the other, or if it is doubtful whether one moved or did not move the other Rabbi Joshua pronounces such a case impure, and the Sages pronounce it pure.