金剛般若經贊述 2.216

2.216

無著云，此第五為語具足故，謂化、報隨機而有言說，法身幽寂無說、無形。內證無言理，外能為他說，為令得此故，言為語具足故也。

Asaṅga says that this is the fifth, for the sake of the perfection of speech. That is to say, the nirmāṇakāya and saṃbhogakāya produce speech in accordance with capacities, whereas the dharmakāya is profound, tranquil, without speech, and without form. Inwardly realising the ineffable principle, outwardly he can speak for others. It is to cause [sentient beings] to attain this that it says 'for the sake of the perfection of speech.'