四明十義書 2.82

2.82

言有佛性者，乃是有於果人之性。既云有於果人之性，故心之與色俱須從因從事而說。既云觀妄心成真心，故知真心須從果說。若論真心，須論真色。已是果法，豈可更別有果性耶？故彼文云：因不名佛，果不名性。今欲示有情有佛性，故須約煩惱心說唯心；欲示無情有佛性，故須約生死色說唯色也。

Saying that they possess buddha-nature means possessing the nature of the person of the fruit. Since it says they possess the nature of the person of the fruit, both mind and form must be spoken of in terms of cause and in terms of phenomena. Since it is said that contemplating the deluded mind accomplishes the true mind, we know that the true mind must be spoken of in terms of the fruit. If one discusses the true mind, one must discuss true form. Since this is already the fruit dharma, how could there be a separate fruit nature? Therefore that text states: "The cause is not called buddha; the fruit is not called nature." Now, wishing to demonstrate that sentient beings possess buddha-nature, one must explain mind-only in terms of the afflicted mind; wishing to demonstrate that insentient beings possess buddha-nature, one must explain form-only in terms of the form of saṃsāra.