大毘盧遮那成佛經疏 14.11

14.11

次以左手單舒散之，如前轉法輪印，但單手不相句絞乃為異耳，此是那羅延天印。

Next, spread and extend the left hand alone, like the previously described wheel-turning mudrā, but done with a single hand without hooking or intertwining—this makes the difference; this is the Nārāyaṇa Deva mudrā.