大般涅槃經義記 8.128

8.128

初中「汝言云何為性」牒舉前問，諦聽許說。下正答之，就中宣說三義為性：一第一義空以為佛性、二智慧為性、三中道為性。

In the initial part, "You say: what is the nature?" takes up and cites the previous question, and by [telling him to] listen attentively, he consents to explain. Below, he directly answers it, wherein he proclaims three meanings as the nature: first, taking ultimate emptiness as the buddha-nature; second, taking wisdom as the nature; third, taking the middle way as the nature.