大毘盧遮那成佛經疏 17.6

17.6

Second, form the mudrā as before, but bend both wind fingers together to touch the tips of the two space fingers, joining so that both resemble the shape of the syllable va; this is the adamantine indestructible mudrā. 'Adamantine' is the Tathāgata's gnosis; not being produced from conditions, it cannot be destroyed, hence it is named 'adamantine indestructible'. Its maṇḍala is round in shape, like the syllable va (which is the fifth vowel of the ba series), surrounded by vajras (which should be vajras with flaming radiance). If one asks about these vajras, they are also on the four sides of the maṇḍala, as above. The so-called syllable va: this maṇḍala is perfectly round and white, and is likewise upon a lotus receptacle. Within it is Mahāvairocana Tathāgata; all below follow this pattern. However, of these eight mudrās, the practitioner takes any one according to need and employs it according to the ritual purpose. Its mantra is: