Miszna do Kapłańska 13:55

A screen that had colored and white stripes, a nega may effectively spread from one to the other. They asked Rabbi Eliezer: But the white stripe is separate? He replied: I have heard no ruling on this question. Rabbi Judah ben Batera said to him: Shall I derive the answer? He replied: If this would confirm the words of the sages, then yes! He said back: It is possible that it would remain on it in an unchanged condition for two weeks, and that which remains unchanged on garments for two weeks is unclean. He said to him: You are a great sage, for you have confirmed the words of the sages. A spreading that is close [to the original nega is effective] however small it may be. One that is distant [is effective only] if it is of the size of a split bean. And one that reappears [is effective only if it is] of the size of a split bean.