大毘盧遮那成佛經疏 14.8

14.8

次以左手申地水火三指令各舒散，以風捻空，此是那羅延后印也（持花印掩胸也，今此印向外掘也）。

Next, with the left hand, extend the three fingers earth, water, and fire, spreading each of them out, and pinch the space finger with the wind finger; this is the Nārāyaṇī mudrā (a holding-a-flower mudrā shielding the chest; here this mudrā is held outward).