Sutra: Great Essence Sutras
The most important sutras or scriptural discourses of the Buddha for understanding tathagatagarbha or Buddhanature are the ten "Essence Sutras."
These ten sutras serve textual basis for zhentong. The Sanskrit names of these sutras are:
Tathagatagarbha Sutra
Arya-dharanish-vararaja Sutra [also known as the ]]Tathagata-maha-karuna-nidesha Sutra]])
Maha-pari-nirvana Sutra
Anguli-malya Sutra
Shri-mala-devi-simha-nanda Sutra
Jnana-loka-lamkara Sutra
Anuna-trapur-natva-nirdesha-parivarta Sutra
Mahab-jeri Sutra
Avi-kalpa-prave-sha-dharani Sutra
Samdhi-nirmochana Sutra
Among these Essence Sutras, the Tathagatagarbha Sutra appears to be the earliest occurrence of the Buddha's teaching on Buddhanature.
The Maha-pari-nirvana Sutra, Shri-mala-devi-simha-nanda Sutra, and Samdhi-nirmochana Sutra were highly influential though appear to be rather late.
In addition to these Essence Sutras, the Avatamsaka Sutra and the Lankavatara Sutra also explain Buddhanature.