大毘盧遮那成佛經疏 14.58

14.58

此三道真言，即攝如來身語意平等法門。然此三真言，若著娑訶字亦得，若不著亦得，行者得意時自看方便也。又復此真言，由最勝故，號之為王。如上說，雖各有四字，然此中相含，但名為十二字真言王也。此中四種輪，各隨彼地水火風輪而加持阿闍梨身即得自在之用。其身口意真言亦合加持自身口意業也。此事未明了（更問之。又云前是布字法，今此中用別計合，是隨五種事相應字即攝彼中之用。更問也）

These three lines of mantras encompass the dharmamukhas of the equality of the Tathāgata's body, speech, and mind. However, regarding these three mantras, it is acceptable if the syllables 'svāhā' are appended, and also acceptable if they are not; when the practitioner grasps the meaning, he may consider the upāya for himself. Furthermore, because this mantra is supreme, it is called a king. As stated above, although each has four syllables, because they are mutually subsumed here, it is simply called the Twelve-Syllable Mantra King. In this, the four wheels empower the ācārya's body in accordance with each of those wheels of earth, water, fire, and wind, whereupon he attains mastery in their function. His body, speech, and mind mantras should also empower his own physical, verbal, and mental karma. This matter is not yet fully clear. (Inquire further into this. It is also said: previously was the method of distributing syllables; now here their use is different, and they should correspond to the five activities, their corresponding syllables subsuming their functions within them. Inquire further.)