維摩經略疏 3.98

3.98

問：何以佛有四種，涅槃但二？答：佛約用智，不同涅槃但約斷德。如云：巧拙兩度，病瘥是一。更開涅槃，非是不得。教無的文。

Question: Why are there four kinds of Buddhas, but only two of nirvāṇa? Answer: 'Buddha' is explained in terms of the function of wisdom, unlike nirvāṇa, which is explained solely in terms of the virtue of severance. As it is said: between the skillful and unskillful two crossings, recovery from illness is one. Opening nirvāṇa further is not impermissible, but the teachings lack a definitive text.