As for their beginningless existence as dharmin and dharmata, the Nirvana Sutra says:
O son of noble family, the nature of mind is naturally luminous and naturally essenceless.
The way naturally pure mind appears is by participating in buddha qualities that blaze with the major and minor marks,
and not being separate from them.
Nevertheless its empty and apparent natures are distinguished.
The established gotra, superimposed on the primordial gotra,
is the incidental upaya and prajña of the four paths of learning.
It is produced by mind and so forth.
Purification occurs through the activities of the two accumulations of merit and wisdom.
The Gandavyuha Sutra says:
Kye, sons of the Victorious One! This which is called the gotra of enlightenment is genuine dharmadhatu. It is vast like the sky. When its naturally luminous nature has been seen, training in accord with the great accumulations of merit and wisdom is purified.
The Uttaratantra says:
Like the buried treasure and the fruit
The two aspects of the gotra should be known
They are the beginningless natural presence
And supremacy that truly is received.
As is taught, arising from these two gotras,
The trikaya of the Buddha is attained.
By the first arises the first of the kayas,
By the second rise the subsequent two.
All the splendor of svabhavikakaya,
Like the precious statue of the Buddha.
Is self-arising and therefore unproduced.
It is a mine of precious qualities.
Because of its great dominion over the dharmin
It is fully expressed, like a universal monarch.
Its phenomenal nature is like a reflection,
With emanation-bodies like forms of gold.
Svabhavikakaya is mind itself, the naturally existing gotra. This is like a naturally existing jewel. From within it comes the gotra with the nature of the dharmin. Here there are the universal monarch of sambhogakaya, and its reflected emanation, arising in dependence on it, nirmanakaya, the supreme emanation for those who are to be tamed.
At the time of existing as a sentient being, these do not appear, because defilement obscures them.
By accumulating merit through visualization and so forth, defilements that obscure rupakaya are cleared away. By the accumulation of wisdom through emptiness meditation and so forth, obscurations are cleared away from the dharmata-svabhavikakaya, the body of the self-existing-essence, the nature of dharmas.
The support, the naturally existing gotra, is like clear water. Within it the supported, the established gotra, rises like a variety of reflections. The two exist primordially, like reflector and reflection.
Within the gotra that exists as the ground, the incidentally established gotra exists as the phenomena of knowing mind, as knowable objects. These are respectively support and supported.
The dharmin exists separably with dharmata, the naturally existing gotra. As a separable fruition, it is non-existent. The produced gotra is an antidote to purify defilements. Though the two kayas exist as if they were produced effect and producing cause, there is no actual causation. That gotra makes the perfect buddha qualities be born as the realization of the paths of learning. This is their liberation or ripening as the level of buddhahood.
The Mahayanasutralankara says:
The nature and the vast extent of its blossoming;
That these exist as support and what is supported;
Their existence and non-existence; their buddha qualities
Are what should be known as the meaning of liberation.
Sugatagarbha pervades all sentient beings. By the nine examples it is taught to exist within the covering of the kleshas.
The Uttaratantra says:
A buddha in a decaying lotus, bees and honey.
Gold within a covering of an unclean nature.
Treasure in the earth, the germ within a fruit,
An image of the Buddha covered up with rags.
A king within the belly of a poor and ugly woman.
Jewels in the earth, within such forms as these,
Obscured by incidental defilements of the kleshas,
This dhatu so exists inside of sentient beings.
These nine examples are related to the obscured dhatu as it exists in ordinary individuals, arhats among the shravakas and pratyekabuddhas, and bodhisattvas dwelling on the paths of seeing and meditation. Ordinary people are those who have not entered into the path; or those who have entered but with their being obscured by the assembly of the four obscurations, passion, aggression, ignorance, and all of these together.
From the four examples of the dhatu within them, first, as for the example of how the essence exists when obscured by propensities of desire, the Uttaratantra says:
Existing in a lotus that is evil-colored,
A Tathagata-statue, blazing with a thousand marks,
Having once been seen with the undefiled eye of the gods,
The statue would be removed from its mud-born lotus cover.
For tathagatas dwelling in places without torment
Their intrinsic buddha eye sees what will later be unobscured.
Their intrinsic endless compassion will free it from obscuration.
Second, the example of the dhatu existing in a covering characterized by propensities of aggression:
Like honey that is surrounded by a swarm of bees,
Capable persons have a wish that they could acquire it.
Having seen it is there, by using skillful means,
They completely free it from the swarm of insects,
To be followed
May all Beings be released from the deluded cognitive veils and apprehend their own Pristine Nature.
Recognize that all the beings' flaws are unreal - mere confused and impermanent appearances, because actually the Buddha Nature is originally perfect.