Kelim, Chapter Twenty-Seven, Mishnah Eigh
1) Similarly, if a piece of cloth was woven to the size of three [fingerbreadths] square, and it contracted corpse uncleanness, and afterwards he finished the entire piece, and then he removed a single thread from its original part, it is free from corpse uncleanness but is still unclean from contact with corpse uncleanness.
2) If a thread was removed from the original part and then all the cloth was finished it remains clean, for the sages have ruled: if a piece of three [fingerbreadths] square is lessened it becomes clean.
3) But if one of three handbreadths square is lessened, even though it is released from midras, it is still susceptible to all other forms of uncleanness.
Section one: This is virtually the same halakhah as was found in section one of yesterday’s mishnah, except that today’s mishnah deals with a smaller piece of cloth, three fingerbreadths square. A piece this size cannot contract midras, but it can contract corpse impurity.
Section two: If a three fingerbreadths piece of cloth contracts corpse uncleanness and then is reduced, it is completely pure. Even if he then enlarges the cloth, there is no impurity left, so the whole cloth is pure.
Section three: This is the difference between the type of impurity contracted by a three fingerbreadths piece of cloth, and one that is three handbreadths. A three handbreadths piece of cloth is still susceptible to other forms of impurity, such as corpse impurity. In contrast, something smaller than three fingerbreadths square is completely pure.