Virtuous man, what is the sign of life? It is the mind of sentient beings that illuminates purity, in which they are aware of what they have realized. Karmic [consciousness] and wisdom cannot perceive themselves. This is comparable to the root of life. Virtuous man, when the mind is able to illuminate and perceive enlightenment, it is but a defilement, because both perceiver and perceived are not apart from defilement. After ice melts in hot water, there is no ice to be aware of its melting. The perception of the existence of the self enlightening itself is also like this.
The Sutra of Complete Enlightenment, p. 51