大毘盧遮那成佛經疏 13.157

13.157

次寶處菩薩印。右手作拳（大指在外者），即舒地水火指並竪之，即是也。

Next is the mudrā of the Bodhisattva Ratnākara. Make a fist with the right hand (with the thumb outside), then extend the earth [little], water [ring], and fire [middle] fingers standing side by side; this is it.