Combine oak ashes, fennel, and musk. Grind until well mixed and as fine as possible. Sprinkle around your altar and around a figure candle representing the one who is cheating. Carry the remainder in a red bag and, if you wish, sprinkle on the underwear of the one you suspect of cheating. It would be better if the candle is consecrated/baptised as the suspected cheater and includes some hair or other material personal to them. Light the candle at sundown on Tuesday at the dark of the moon or as soon after as it falls, burn for an hour. Continue, each Tuesday at sundown, until the full moon. Burn the rest of the candle that night. You should know before the next full moon.