大毘盧遮那成佛經疏 2.66

2.66

The thirty-seventh: "What is the owl mind? It is constantly thinking in the dark night." This bird is powerless in broad daylight, but at night its six faculties are sharp and clear. If a practitioner hears something during the day, reciting and practicing it in confusion without mastering its subtlety, but in the dark night reflects on what was done, weighing it repeatedly and thereby attaining clarity, even regarding the dark as superior for cultivating dhyāna-contemplation and the like; when one realizes this, one should reflect on the equality of light and darkness, making one's mental application free from the distinction of day and night; this serves as its antidote.