Buddha-nature in all beings dwells permanent and unalterable, throughout all rebirth, ever ready to develop itself as soon as the opportunity arises. (Nirvana Sutra Ch. 26, quoted Hobogirin II, 185ff, EB “Buddha-Nature”)

When the Buddha Śākyamuni first realized Buddhahood, he proclaimed:

How amazing! How amazing! How amazing! All living beings have the Buddha-nature; all can become Buddhas. Only because of their polluted thinking and attachments do they fail to realize this and to obtain certification.

The supreme, pure bright mind originally pervades the Dharma Realm. It is not something obtained from anyone else. Why, then, labor and toil with marrow and joint to cultivate and be certified? This is to be like the person who has a wish-fulfilling pearl sewn in his clothing without realizing it. Thus he roams abroad in a state of poverty, begging for food and always on the move. Although he is indeed destitute, the pearl is never lost. Suddenly a wise person shows him the pearl: all his wishes are fulfilled, he obtains great wealth, and he realizes that the pearl did not come from somewhere outside. (SS IV 108-111)

“Showing him the pearl in his clothing represents pointing out to him his inherent Buddha-nature.” (SS IV 111)

佛性