大毘盧遮那成佛經疏 13.211

13.211

佛眼印，如前佛母印作之。是中少許異者，謂開空指令去火指背一麥許不相著，如似五股之形即是也。

Make the Buddhalocanā mudrā as the Buddha Mother mudrā was made before. The slight difference here is that the space fingers are separated from the backs of the fire fingers by about the width of a barleycorn without touching, taking a five-pronged shape—that is it.