大般涅槃經義記 8.187

8.187

第二舉說證皆有中，「以是義故我常宣說一切有」者釋有通別。通則以前未來有故，說一切生悉有佛性。

In the second point, citing the teaching to verify that all possess it: 'For this reason, I constantly proclaim that all possess it' explains existence as general and specific. In the general sense, based on the aforementioned future existence, it says that all living beings possess buddha-nature.