כָּל־יְמֵ֞י אֲשֶׁ֨ר הַנֶּ֥גַע בּ֛וֹ יִטְמָ֖א טָמֵ֣א ה֑וּא בָּדָ֣ד יֵשֵׁ֔ב מִח֥וּץ לַֽמַּחֲנֶ֖ה מוֹשָׁבֽוֹ׃ (ס)
All the days wherein the plague is in him he shall be unclean; he is unclean; he shall dwell alone; without the camp shall his dwelling be.
Mishnah Negaim
If one had a bright spot and it was cut off, he becomes clean; If he cut it off intentionally: Rabbi Eliezer says: [he is clean] only after another nega arises in him and he has attained cleanness after it. But the sages say: only after it has spread over all his body. If it was on the tip of one's foreskin, he should be circumcised.
Mishnah Negaim
If an unclean person stood under a tree and a clean person passed by, the latter becomes unclean. If a clean person stood under a tree and an unclean one passed by, the former remains clean. If the latter stood still, the former becomes unclean. Similarly in the case of a leprous stone he remains clean. But if it was set down he becomes unclean.