Good son, there are three ways of having: first, to have in the future, Secondly, to have at present, and thirdly, to have in the past. All sentient beings will have in future ages the most perfect enlightenment, i.e., the Buddha nature. All sentient beings have at present bonds of defilements, and do not now possess the thirty-two marks and eighty noble characteristics of the Buddha. All sentient beings had in past ages deeds leading to the elimination of defilements and so can now perceive the Buddha nature as their future goal. For such reasons, I always proclaim that all sentient beings have the Buddha nature.
Heng-Ching Shih, "The Significance Of 'Tathagatagarbha' -- A Positive Expression Of 'Sunyata.'" http://zencomp.com/greatwisdom/ebud/ebdha191.htm