瑜伽師地論略纂 4.134

4.134

又，三謂三界。三界之中，發現纏之隨眠無明滅故，現無明滅；現無明滅故，一切行滅。無明為首，獨說三界。

Furthermore, 'three' refers to the three realms. When, within the three realms, the dormant ignorance that manifests active entanglements is eliminated, active ignorance is eliminated; because active ignorance is eliminated, all formations are eliminated. Taking ignorance as foremost, the three realms alone are stated.