On Buddha-nature:

"As is stated in the King of Meditative Absorption Sutra:

The Essence of the Well-gone One pervades all migrators.

The Small Parinirvana Sutra says:

All sentient beings have the Essence of the Thus-gone One.'

Also, the Sutra of the Great Parinirvana says:

For example, as butter permeates milk, likewise the Essence of the Thus-gone One pervades all sentient beings.

And in the Ornament of Mahayana Sutra:

Even though suchness is not different for any being, One is called "Thus-gone One" when it is fully purified. Therefore, all beings are of its essence."