摩訶止觀 6.161

6.161

若得此意，料簡變化即識真偽。所以者何？魔亦能以有漏心作無漏形，變為佛像。老子西升，亦云作佛化胡；諸外道等變釋為羊，停河在耳。世智五通靡所不作，如是邪化無量無邊。尚非三藏五通化，云何得是別圓任運真化？化語多種，無眼之人謬生信受。能深觀察，不可雷同。故知從法身地，垂應十界度脫眾生，如此入假，真利益位。

If one grasps this meaning, in examining transformations one immediately recognizes the true and the false. Why is that? Māra can also use a tainted mind to make an untainted form, transforming into an image of a Buddha. When Laozi ascended to the west, it is also said that he became a Buddha to convert the barbarians; various tīrthikas transformed Śākyamuni into a sheep, or held a river in an ear. With worldly wisdom and the five supernormal powers, there is nothing they cannot do; such heterodox transformations are immeasurable and boundless. These are not even the transformations of the five supernormal powers of the Tripiṭaka teaching; how could they be the spontaneous true transformations of the distinctive and perfect [teachings]? The discourses on transformation are of many kinds, and people without eyes mistakenly give rise to faith and acceptance. If one can deeply observe, they cannot be lumped together as identical. Therefore, know that extending responses to the ten realms from the ground of the dharmakāya to deliver sentient beings—entering the provisional in this way is the stage of true benefit.