佛頂尊勝陀羅尼經教跡義記 2.63

2.63

唐云契印。解曰：契印者，諸佛如來契約印信，契即是發，印即是驗，所謂身印百千威儀，語印無量真言，心印塵沙觀智，一一指歸金剛祕決，於阿闍梨伏膺受訓，當自明了之。

In Chinese it means: "Mudrā." The explanation states: A "mudrā" is the covenant and sealed certificate of all Buddhas and Tathāgatas: the covenant is the arising, and the seal is the verification. Namely, the body mudrā comprises the hundreds of thousands of deportments; the speech mudrā comprises the immeasurable mantras; the mind mudrā comprises the contemplation-wisdoms as numerous as dust and sand. Each and every one points back to the esoteric secrets of the vajra. Submitting oneself before the ācārya to receive instruction, one will understand it for oneself.