PJ Num19:18↗ויטמוש במיא האינון בעידן קיבול סובתאwyṭmwš bmyˀ hˀynwn bˁydn qybwl swbtˀܘܝܛܡܘܫ ܒܡܝܐ ܗܐܝܢܘܢ ܒܥܝܕܢ ܩܝܒܘܠ ܣܘܒܬܐܘܝܛܡܘܫ ܒܡܝܐ ܗܐܝܢܘܢ ܒܥܝܕܢ ܩܝܒܘܠ ܣܘܒܬܐwyṭmwš bmyˀ hˀynwn bˁydn qybwl swbtˀויטמוש במיא האינון בעידן קיבול סובתאܘܝܛܡܘܫ ܒܡܝܐ ܗܐܝܢܘܢ ܒܥܝܕܢ ܩܝܒܘܠ ܣܘܒܬܐܘܝܛܡܘܫ ܒܡܝܐ ܗܐܝܢܘܢ ܒܥܝܕܢ ܩܝܒܘܠ ܣܘܒܬܐ: let him immerse them in that water when the time is right for receiving uncleanliness †
For the numerous issues only briefly alluded to in the PsJon citation, see Mishnah Parah, chapters 6ff., esp. chapter 12. The hyssop, the water, and the priest all must might stringent requirements for the magic to work!