四分律刪繁補闕行事鈔 2.363

2.363

言能持者，用心為體，身口是具。故論云：是三種業，皆但是心。又律云：備具三種業，當審觀其意等。如後更解。

Regarding the agent of observance: the mental application is the essence, while body and speech are the instruments. Therefore the treatise states: "These three kinds of karma are all merely mind." The Vinaya also states: "Having fully prepared the three kinds of karma, one should carefully examine their intention," and so forth, as will be explained further below.