觀音玄義 2.43

2.43

問：為用法身應？為用應身應？應身無常，此則無應；法身若應，此則非法身。答：法既言身，何不言應？應身既稱應，何意不應？故俱應。

Question: Does one respond using the dharma-kāya, or using the responsive body? The responsive body is impermanent, so here there is no response; if the dharma-kāya responds, then it is not the dharma-kāya. Answer: Since the Dharma is called a body, why should it not be called responsive? Since the responsive body is termed responsive, why should it not respond? Therefore, both respond.