TT #255 · Parshas Tazria · Aliyah 7 · Passuk 46
English: All the days that the affliction is upon him he shall be impure; he is impure. He shall dwell alone; his dwelling shall be outside the camp.
Torah Temimah cites Mishnah Negaim 13:7 for the rules governing a pure and impure person under a shared tree.
English: The Mishnah distinguishes the two arrangements: if the impure person sits beneath the tree while the pure person stands there, the pure person becomes impure; if the pure person sits and the impure person stands, the pure person remains pure.
Textual derivation
The Mishnah distinguishes the effects of sitting and standing under a shared shelter in the laws of impurity.