Tibetan Chan II: the teachings of Heshang Moheyan

"When you are engaged in contemplation itself, look at your own mind. Then, the lack of any mental activity at all is non-thought. If there is movement of the conceptual mind, be aware of it. “How should one be aware?” Do not analyse the mind which is moving in terms of any kind of quality at all: do not analyse it as moving or not moving; do not analyse it as existing or not exising; do not analyse it as virtuous or non-virtuous; and do not analyse it as defiled or pure. If you are aware of mind in this way, it is natureless. This is the practice of the dharma path."

http://earlytibet.com/2008/05/15/tibetan-chan-ii-the-teachings-of-heshang-moheyan/