首楞嚴義疏注經 4.160

4.160

覺性如地，惑障如木，加行如燧，智照如火，涅槃如灰。燧動火起，木盡灰成，灰歸於地，不重為木。修行智起，惑滅覺顯，顯處唯真，不重起妄。

The nature of enlightenment is like the earth; afflictive hindrances are like wood; preparatory practice (prayogamārga) is like the fire-drill; the illumination of wisdom is like fire; nirvāṇa is like ash. When the fire-drill moves, fire arises; the wood is consumed and ash is formed; the ash returns to the earth and never again becomes wood. When the wisdom of cultivation arises, delusion is eliminated and enlightenment is revealed; where it is revealed, it is purely real and delusion never arises again.