Psalm 51:7. Purge me with hyssop, and I shall be clean.
Hyssop was appointed to be used in ceremonial purification. It was used in connection with the passover (Ex. 12:22), the cleansing of lepers (Lev. 14:4,6,49,51,52), and the sacrifice of the red heifer (Num. 19:6,18). See also Hebrews 9:19. Hyssop was anciently considered a means of actual bodily purification, and was even taken internally for that purpose.