Parah 12:6

Let’s say that someone sprinkled using ritually-unclean hyssop. If the hyssop was the size of an egg, the water is invalidated and the sprinkling is invalid. If it was smaller than the size of an egg, the water remains fit but the sprinkling is invalid. It also renders other hyssop unclean, and that other hyssop conveys impurity to still more hyssop, even if there are 100 of them.

Parah 12:7

If the hands of a person who was ritually clean for the sanctification water were rendered unclean, his body is also rendered unclean and he transmits ritual impurity to another person, and that person to still another person, even if there are 100 of them.