大毘盧遮那經阿闍梨真實智品中阿闍梨住阿字觀門 1.21

1.21

阿闍梨若持念時或觀句輪。句輪者，觀本尊心有圓明而布真言之字，輪轉相接明了現前；觀此字輪猶如白乳，次第流注入行者口中，或注其頂，相續不絕遍滿其身。其圓明中有種子字，字常明了，猶如流水無盡。如是持誦疲極已，即但住於寂心阿字。

When the ācārya engages in recitation, he may contemplate the sentence wheel (padacakra). As for the sentence wheel: one contemplates the heart of the deity having a round radiance in which the letters of the mantra are arranged, turning like a wheel and joined end to end, clearly manifesting before oneself. One contemplates this wheel of letters as being like white milk, pouring continuously into the practitioner's mouth or flowing into his crown, uninterruptedly filling his whole body. Within that round radiance is the seed syllable (bīja), which is always distinct, like water flowing without end. When he is thoroughly exhausted from reciting in this manner, he merely abides in the quieted mind of the letter A.