首楞嚴義疏注經 4.266

4.266

直明妄無因也。妄必無因，有因不妄，妄之一字甚好思量。若了此名，自無法起，復疑有因，豈非迷倒？如初一人忽然妄說，遞遞相承從妄說妄，及推其本，遞遞皆虛，乃至初人及與後人二俱是妄，何者為因？故歷塵劫，遞相誑妄，莫之能悟。

This directly clarifies that delusion has no cause. Delusion must have no cause; if it had a cause, it would not be delusion. The single word 'delusion' is very worthy of contemplation. If one understands this name, naturally no dharma arises; if one still doubts that there is a cause, is that not being deluded and inverted? Like a first person who suddenly spoke falsely, and one after another handed it down, speaking delusion from delusion: when tracing its root, each in succession is completely baseless, up to both the first person and the later person being deluded. What could be the cause? Therefore, passing through kalpas as numerous as dust motes, they deceive one another with delusion, and none is able to awaken.