This quote is suspect, seeming to have resulted from two separate statements having bee joined together. When I saw the first part I recognized it as stemming from the Dhammapada:
Enduring patience is the highest austerity.
“Nibbana is supreme,” say the Buddhas.
He is not a true monk who harms another,
nor a true renunciate who oppresses others.
So the first line more or less matches the start of the quote, but obviously there’s nothing in here about victory. The Dhammapada does have a few things to say about victory, including that the Buddha’s victory is not turned into defeat (verse 179), and a variant of this saying that no one (not even the gods or Māra) can turn the Buddha’s victory into defeat (verse 105), and also that the Buddha has abandoned victory and defeat (verse 201). But I haven’t found anything in the Dhammapada or elsewhere that corresponds to “it is to the one who endures that the final victory comes.”
There are passages that are somewhat similar to “it is to the one who endures that the final victory comes,” including:
Whoever doesn’t flare up
at someone who’s angry
wins a battle
hard to win.
Thematically, at least, this verse concerns patience and victory.
And there’s a faint resonance of this line in verse 5 of the Dhammapada:
Hatred is never appeased by hatred in this world. By non-hatred alone is hatred appeased.
“Non-hatred” includes patience, and “appeased” could just about be read as “conquered” and so we’re close to the semantic territory of “victory.”
In the Samyutta Nikaya there’s a verse that goes:
The fool thinks victory is won
When, by speech, he bellows harshly;
But for one who understands,
Patient endurance is the true victory.
The last two lines pair patience and victory, and the last line is close enough to “it is to the one who endures that the final victory comes” that I think it’s acceptable as a variant translation.
So both parts of the quote have close parallels in the Pali canon, with “Endurance is one of the most difficult disciplines” corresponding to “Enduring patience is the highest austerity” and “it is to the one who endures that the final victory comes” corresponding to “patient endurance is the true victory.” The variation in wording isn’t too surprising given that the texts have been translated from an Indian language into Chinese or Japanese, and then back into English.
So this quote, taken as a whole, is in a kind of gray area. The parts are more or less genuine, but the seem to have been cobbled together, which makes the quote as a whole suspect (or fake). Where did the cobbling take place?
The full quote is from a Japanese book called Teaching of Buddha, which is the Buddhist equivalent of the Gideon Bible, in that it’s found in hotel bedrooms throughout the world. But it differs from the Gideon Bible in that it’s not a straightforward presentation of scripture. There are, for example, verses like this one, which appear to be a combination of canonical passages and commentary. There are also some parts of Teaching of Buddha that are pure commentary — essays on Buddhism, rather than Buddhist scripture — but in some cases people have been misled by the book’s title into thinking that the commentary is scripture.
It’s possible that in some Far Eastern scripture, these two separate sayings were put together. Sometimes when the Indian texts were translated into Chinese, for example, there would be some rewriting and rearranging. And my position on accepted scripture is that it’s “genuine,” so if this quote does exist in a Chinese version of a sutra then it would be genuine. At the moment it remains suspect.