Mahayana Mahaparinirvana Sutra
The Mahayana Mahaparinirvana Sutra, as translated into English by Kosho Yamamoto and edited and revised by Dr. Tony Page (Nirvana Publications, London, 1999-2000).

That the Buddha-Principle (Buddha-dhatu) or Buddha-Matrix (Tathagatagarbha) is the essence (svabhava) or Dharmakaya (ultimate level of being) of the Buddha and of all persons and creatures, in contrast to the five skandhas (impermanent components which make up the “mundane ego”); the Buddha-dhatu is the “True Self”, which inheres in the Buddha’s deepest being, as well as being truly present in our own body-and-mind complex, and into which we should “enter”. Such “entry” is enabled when we have cleared away the kleshas (negative mental, moral and behavioural tendencies) from our inner world. The chief kleshas are desire, anger, delusion and pride.” — © Dr Tony Page 2004