เลวีนิติ 14:28

על מקום דם האשם UPON THE PLACE OF THE BLOOD OF THE GUILT-OFFERING — even though the blood has been wiped off; this teaches that it is not the presence of the blood that brings about the validity of this rite but it is the place (the fact that the oil has been placed on the proper spot) that brings it about (Sifra, Metzora, Chapter 3 10; Menachot 10a).

and the priest shall put of the oil that is in his hand upon the tip of the right ear of him that is to be cleansed, and upon the thumb of his right hand, and upon the great toe of his right foot, upon the place of the blood of the guilt offering:

וְנָתַ֨ן הַכֹּהֵ֜ן מִן־הַשֶּׁ֣מֶן ׀ אֲשֶׁ֣ר עַל־כַּפּ֗וֹ עַל־תְּנ֞וּךְ אֹ֤זֶן הַמִּטַּהֵר֙ הַיְמָנִ֔ית וְעַל־בֹּ֤הֶן יָדוֹ֙ הַיְמָנִ֔ית וְעַל־בֹּ֥הֶן רַגְל֖וֹ הַיְמָנִ֑ית עַל־מְק֖וֹם דַּ֥ם הָאָשָֽׁם׃