Kelim, Chapter Six, Mishnah Two
1) A stone on which he placed a pot, [on it] and on an oven, or on it and a double stove, or on it and on a stove, is susceptible to impurity.
2) [If he set the pot] on it and on another stone, on it and on a rock, or on it and on a wall, it is not susceptible to impurity.
a) And such was the stove of the Nazirites in Jerusalem which was set up against a rock.
3) As regards the stove of the butchers, where the stones are placed side by side, if one of the stoves contracted impurity, the others do not become unclean.
Section one: In this case a person places a pot on a makeshift stove, where one side consists of a stone attached to the ground by clay and the other side consists of either an oven a double stove or a single stove. The stone is susceptible to impurity in this case because the oven or stove counts as a second attached stone. This is similar to the situation in yesterday’s mishnah.
Section two: In this case he sets the other side of the pot not on another oven or stove, but on another stone which was unattached to the ground with clay or on a rock which was part of the ground, or on a wall. These do not count as a “second stone attached to the ground” which as we learned in yesterday’s mishnah causes both stones to be susceptible to impurity. Rather in this case the stone which is attached to the ground with clay is susceptible.
At the end of his/her term of naziriteship a nazirite must bring a shelamim offering. To prevent the sacrifice from being defiled, they would cook it in a stove made of one stone attached to the ground and the other side of the pot resting on the wall.
Section three: Butchers would make a line of stoves made of stones attached to the ground. Each stone, except for the outer ones, could be used to hold up two pots, one to the left and one to the right. The mishnah looks at each pair of stones as an independent unit such that if one stone becomes impure, the pair next to it retains its purity.