Keilim 27:8-9

Keilim 27:8

Let’s say that a piece of cloth of which one has woven three fingerbreadths by three fingerbreadths contracts corpse impurity and he then completes the garment. If one then removes one thread from the original part, the garment is purified of corpse impurity (the part that was rendered impure having been reduced in size) but it remains unclean from contact with corpse impurity. If he removed a thread from the original part and only subsequently completed the garment, the garment is ritually clean. This is because the Sages have said that if a piece of cloth three fingerbreadths by three fingerbreadths is reduced in size, it is purified but if one three handbreadths by three handbreadths is reduced, even though it is free from midras, it remains susceptible to all other forms of impurity.

Keilim 27:9

If a sheet that had contracted midras impurity was made into a curtain, it is cleansed of midras impurity but is remains unclean from contact with midras impurity. Rabbi Yosi asks what midras the curtain has touched; only if a zav touched it is it impure from contact with a zav.