וְלָקַ֞ח אֶלְעָזָ֧ר הַכֹּהֵ֛ן מִדָּמָ֖הּ בְּאֶצְבָּע֑וֹ וְהִזָּ֞ה אֶל־נֹ֨כַח פְּנֵ֧י אֹֽהֶל־מוֹעֵ֛ד מִדָּמָ֖הּ שֶׁ֥בַע פְּעָמִֽים׃
And Eleazar the priest shall take of her blood with his finger, and sprinkle of her blood toward the front of the tent of meeting seven times.
Read kabbalistic (mystical) interpretation of Numbers 19:4: and classical mystical sources.