大毘盧遮那經廣大儀軌 2.146

2.146

右白蓮華中，觀蘖丹（郗痕反）字光輪，
轉成清淨慧。如前商佉印。

In the white lotus on the right, visualize the light-wheel of the syllables gagan,
which transforms into Viśuddhamati;
[the mudrā is] like the conch mudrā described before.