Negative Mitzvah 12: You shall not have kneeling stones
Leviticus 26:1 "Nor shall you install a kneeling stone in your land,
to bow down upon it"
Idol-worshipers often placed a special decorated stone before their
idol and then use it to kneel upon while they prayed to their idols.
We are forbidden to have such a stone, even if we intend to worship
HaShem on it.