"The perfect buddhakaya is all-embracing, suchness cannot be differentiated, and all beings have the disposition. Thus they always have buddha nature. The Buddha has said that all beings have buddha nature since buddha wisdom is always present within the assembly of beings, since this undefiled nature is free from duality, and since the disposition to buddhahood has been named after its fruit."

Mahāyānottaratantra Śāstra;