משנה אויף במדבר 9:13

There are in the Torah thirty-six [transgressions which are punishable with] karet:When one has intercourse with his mother, His father's wife; Or his daughter-in-law; When a man has intercourse with a male, Or with a beast, Or when a woman brings a beast upon herself; When one has intercourse with a woman and her daughter; Or with a married woman; Or with his sister; Or with his father's sister; Or his mother's sister; Or his wife's sister; Or his brother's wife; Or the wife of his father's brother; Or with a menstruating woman; One who blasphemes [the Lord]; One who worships idols; Or dedicates his children to Molech; Or has a ba’al ov; Or desecrates the Shabbat; When an unclean person eats of sacred food; Or when one enters the precincts of the Temple in an unclean state; When one eats forbidden fat, Or blood; Notar; Or piggul; When one slaughters Or offers up [a consecrated animal] outside [the Temple]; One who eats anything leavened on Pesah; One who eats Or works on Yom Kippur; One who compounds the oil [of anointing]; Or compounds incense; Or uses [unlawfully] oil of anointing; And [when one transgresses the laws of] the pesah, And circumcision from among positive commandments.

A kokhin field may neither be planted nor sown, but its earth is regarded as clean and ovens may be made of it for holy use. Bet Shammai and Bet Hillel agree that it [a bet peras in which a grave was plowed over] is examined for one who wished to perform the pesah sacrifice,but is not examined for one who wants to eat terumah. And as for a nazirite: Bet Shammai say: it is examined, But Bet Hillel say: it is not examined. How does he examine it? He brings earth that he can move, and places it into a sieve with fine meshes, and crumbles. If a bone of barley-corn size is found there [the person passing through the field] is deemed unclean.