
The Sutra Spoken by the Sixth Patriarch on the High Seat of the Treasure of the Law, otherwise known as The Platform Sutra of Hui-neng.
Hui-neng's life-story was fortunately preserved for us in the sutra text, in the record of his first public talk, which he began as follows:
Learned Audience, our essence of mind [literally, self-nature], which is the seed or kernel of enlightenment [bodhi], is pure by nature, and by making use of this mind alone, we can reach buddhahood directly. Now let me tell you something about my own life and how I came into possession of the esoteric teaching of the Dhyana school.
Hui-neng said that when he heard the sentence "One should use one's mind in such a way that it will be free from any attachment," he "at once became thoroughly enlightened and realized that all things in the universe are the essence of mind itself."
http://www.selfdiscoveryportal.com/ChanMasters.htm
http://www.empty-universe.com/prajnaparamita/heartsutra.htm