大般涅槃經義記 8.281

8.281

第三句中，「若菩提心是佛性」者，逆取佛意。下對徵破。一闡提等不應能斷，是一徵也。佛性常法云何可斷，若可斷者云何言常？是二徵也。若非常者不名佛性，是三徵也。

In the third clause, "If the bodhicitta is the buddha-nature" anticipates the Buddha's intention. Below, he confronts it to interrogate and refute: That icchantikas and the like should not be able to sever it is the first interrogation. How could the buddha-nature, a permanent dharma, be severed? If it can be severed, how can it be called permanent? This is the second interrogation. If it is not permanent, it is not called the buddha-nature; this is the third interrogation.