大毘盧遮那成佛經疏 10.155

10.155

次結大界真言。如佛所說，更有無量持明，恐更有持真言者等以不結護故，能破法事、損持誦人，故設結界之法。由結界故，乃至諸持明亦不能破壞。猶比丘結界作法事，在界外比丘雖作法不能障破也。隨方皆遍也。

Next is the mantra for binding the great boundary. As the Buddha stated, there are further immeasurable vidyādharas; fearing that other mantra-holders and the like might break the ritual acts and harm the reciter due to not establishing a sīmābandha, he set forth the method of binding boundaries. Through binding the boundary, even all vidyādharas cannot break or ruin it. It is like a monk binding a boundary to perform ritual acts; although monks outside the boundary perform rituals, they cannot obstruct or break them. It pervades in every direction.