大毘盧遮那成佛經疏 14.16

14.16

次如前羂索印（謂作內相叉拳而申風指鉤屈相捻是也），但以左手作之，即是縛嚕拏龍王印。

Next, as with the previous pāśa mudrā (meaning, make an inward-interlocking fist, extend the wind fingers hooked and curved to pinch each other), perform it with the left hand alone, and that is the Varuṇa Nāgarāja mudrā.