大毘盧遮那成佛經疏 13.153

13.153

次不思議惠菩薩印。以施無畏手，空風指相捻如執珠之狀也（其手當側之，如擬人合指捻珠。珠向上也。又中指稍相離而向內，餘二指並竪之也）。

Next is the mudrā of the Bodhisattva Acintyamati. With the fear-granting hand, pinch the space [thumb] and wind [index] fingers together like holding a jewel (the hand should be tilted to the side, like someone joining fingers to pinch a jewel, with the jewel pointing upward; furthermore, the middle finger is slightly separated and turned inward, while the other two fingers stand erect side by side).