Midrasch zu Wajikra 13:53

4) (Vayikra 13:53) "And the Cohein shall see, and, behold, the plague-spot has not spread in the garment, or in the warp or in the woof, or in any article of skin": This refers to the stationariness (omed) of the plague-spot, (and not to the non-appearance of a different plague-spot). (Vayikra 13:54) ("Then the Cohein shall command, and they shall wash what contains the plague-spot, and he shall quarantine it a second seven days.") "Then the Cohein shall command and they shall wash": the command, by the Cohein; the washing, by any man.

5) "and they shall wash … the plague-spot": I might think the plague-spot alone; it is, therefore, written "what contains the plague-spot." How so? Some of the adjoining material is washed with it.

6) "and he shall quarantine it a second seven days": We are hereby taught that the seventh day is included in the count — both before it and after it (i.e., the last of the first seven, and the first of the second seven.)