The Diamond Sutra

A Mahāyāna sutra of the Perfection of Wisdom family, set as a dialogue between the Buddha and his disciple Subhūti near Śrāvastī. Subhūti asks how someone who sets out on the bodhisattva path should stand and control the mind. The Buddha answers that a bodhisattva vows to lead all beings to nirvana, yet must not think that any being is led there, and is no bodhisattva if he holds the idea of a self, a being, a soul or a person. Giving should be practised without dwelling on signs. The Buddha cannot be recognised by his bodily marks, and his teaching is like a raft, to be let go of once the river is crossed. A repeated pattern, saying that what is called X is not X and is therefore called X, unsettles fixed concepts. Preserving even four lines of the sutra is said to bring more merit than vast gifts. It ends by comparing all conditioned things to a dream, a bubble, dew and lightning.

It trains the reader to hold ideas without clinging to them, it mattered greatly to Chan and Zen, and a copy printed in 868 is the oldest dated printed book known.