大毘盧遮那經廣大儀軌 2.181

2.181

次左蓮華中，觀怛陵（二合）字法門，
一切法如本，自性無垢身，
光明遍十方，轉成火聚頂。
印與佛頂同。

Next, in the lotus on the left, visualise the syllable triṃ dharma-gate,
All dharmas being fundamentally spotless by intrinsic nature,
Their radiance pervading the ten directions, transforming into Tejoraśy-uṣṇīṣa.
The mudrā is identical to that of the Uṣṇīṣa Buddhas.