大般涅槃經義記 8.257

8.257

自下第二，師子以其非異因生證乳有酪，如來對破。有二問答。師子初言「若乳無酪，角中亦無，何不從生」舉異因難。下佛印取角亦生酪。「何以」下釋，「角性煖故」為緣生酪。如來何意說角生酪？為欲將角類顯乳故。類之云何？角能生酪，角中無酪；乳中生酪，何得有酪？「師子」下，以人取為難：「若角生酪，求酪之人何不取角」。下佛為釋，我說二因，角緣非正，故人不取。

From here below is the second [major section]: Siṃhanāda adduces the fact that [curds] are not produced from a different cause to prove that milk contains curds, and the Tathāgata refutes it in response. There are two questions and answers. First, Siṃhanāda says: "If milk has no curds and horns also have none, why are they not produced from [horns]?"—raising a different cause as a challenge. Below, the Buddha assents, accepting that horns also produce curds. Below "For what reason?", it explains: "Because the nature of horns is warm," they serve as an auxiliary condition to produce curds. With what intention does the Tathāgata say that horns produce curds? It is because he wishes to use horns as an analogical illustration of milk. How are they analogous? Horns can produce curds, yet there are no curds in horns; curds are produced from milk, so how could there be curds [pre-existing] in it? Below "Siṃhanāda", he raises a challenge based on human procurement: "If horns produce curds, why does a person seeking curds not procure horns?" Below, the Buddha explains for him: I have spoken of two causes; the horn is an auxiliary condition and not the primary cause, and therefore people do not procure it.