大毘盧遮那經阿闍梨真實智品中阿闍梨住阿字觀門 1.18

1.18

行者相應如是，布字持念即是持明之身，猶如大日如來神力加持，等無有異，此輪亦名因緣輪；師及弟子并曼荼羅皆如是安布諸字，亦名祕密之輪；此諸字亦是一切佛心之字，亦名真言之輪。

When the practitioner achieves correspondence in this manner, distributing the syllables and reciting mantras, their body is the body of the Vidyādhara, identical and without difference to the empowerment of Mahāvairocana Tathāgata's divine power. This wheel is also named the wheel of causes and conditions; when master, disciple, and maṇḍala all have the syllables arranged in this way, it is also named the secret wheel; these syllables are also the syllables of all Buddha-minds, and it is also named the wheel of mantras.