瑜伽論記 7.179

7.179

四神足者，以別境中定數為體，此定能發五神通，是神通因故，說此定名為神足，此之神足為四法求成，名四神。

As for the four bases of psychic power, they take the mental factor of concentration among the specific object-determining factors as their entity; this concentration can generate the five supernormal knowledges, and being the cause of supernormal knowledges, this concentration is called a base of psychic power; this base of psychic power is sought and accomplished through four dharmas, hence called the four supernormal [bases].