大毘盧遮那成佛經疏 13.67

13.67

次結大界印。准前如來鉤印法，但二手各舉水指令直竪，即是也（更問之，不分明）。此中大界者，謂從發大菩提心乃至成佛，於其中間不令間斷，不復生死、不退菩提，即是大界義也。真言歸命如前。

Next is the Seal of Binding the Great Boundary. Based on the method of the Tathāgata's hook seal above, simply raise the water finger of each of the two hands to stand straight up; that is it (inquire further into this, as it is not clear). The 'great boundary' here means from the initial generation of the great bodhicitta up to the attainment of buddhahood, having no interruption in the interim, neither returning to saṃsāra nor retrogressing from bodhi; this is the meaning of the great boundary. The homage of the mantra is as before.