大毘盧遮那成佛經疏 13.59

13.59

次如來臍印。亦准於前加舒水指，凡舒三指亦屈第三節也。真言歸命如上。

Next is the Tathāgata's Navel Seal. Based also on the preceding, add the extension of the water finger; altogether three fingers are extended and also bent at the third joint. The homage of the mantra is as above.