大般涅槃經集解 67.92

67.92

案僧亮曰：八道火相者，無漏能燒煩惱名火，煖法為因故名相也。寶亮曰：答第二問，明是八聖道之相故名煖，如攢火先有煖也。

Sengliang comments: Regarding the 'fire-signs of the Eightfold Path', the undefiled [wisdom] can burn up the afflictions and is thus called 'fire'. The dharma of heat serves as its cause, and is therefore called its 'sign'. Baoliang comments: In answering the second question, it is explained that because it is a sign of the Eightfold Noble Path, it is called 'heat', just as when drilling for fire, heat appears first.