Let’s nip this one in the bud. It was passed on to me by someone who had spotted it on the Facebook page of The Blue Buddha Quote Collective, where it had been attributed to the Buddha. The Collective seems to have a rather liberal sense of what the Buddha might have said, judging by some of the other quotes they’ve posted.
“We have to understand the middle path: That a human has a positive and a negative side. We have a false, ignorant side, but we also have a beautiful potential – Buddha nature.”
~ The Buddha
The historical Buddha, of course, never talked about Buddha Nature, which is a relatively late teaching, dating from long after his death. So the mere mention of that term rules it out as a saying from the Pali canon. But certain Mahayana Sutras do discuss Buddha Nature (Tathagathagarbha, which is more literally “The Womb of the Buddha”) so that in itself doesn’t rule it out as canonical. The Mahayana Sutras may not have been spoken by the Buddha, but my definition of a Fake Buddha Quote is that it’s a non-canonical saying that’s been attributed to the Buddha.
But … and I have a big “but” (that’s an intentional joke, by the way)…
“Positive” and “negative” are not terms that the Buddha — whether the Buddha of the Pali canon or of the Mahayana Sutras — would have used. He sometimes talked, especially in poetry, of “puñña and papa” (good and evil) and of actions being “kusala or akusala” (skillful or unskillful) but “positive and negative” as ethical categories are strikingly modern.
A Google search reveals several sources saying that this is a quote from Lama Yeshe, and I’m inclined to believe them, especially since one of the sources is the late Lama’s Pinterest page.