大毘盧遮那成佛經疏 13.84

13.84

次如來四辯印。作三補吒合掌，以二風指勾曲當二火指背上，頭勿相著，即是也。如來由此印故，處眾無畏，為人演說正法，乃至於一字中含無窮義，此辯才不可窮盡也。真言歸命如前。

Next is the Tathāgata's Fourfold Eloquence Seal. Make the sampuṭa añjali, hook the two wind fingers over the backs of the two fire fingers without letting their tips touch; that is it. Because of this seal, the Tathāgata abides fearlessly among the assembly, expounding the true Dharma to people, to the extent that a single syllable contains inexhaustible meanings; this eloquence cannot be exhausted. The homage of the mantra is as before.