“Beware the wrath of a patient adversary.”
This has recently become attributed to Calhoun on the internet and in print, but seems to be a derivative of John Dryden's statement in Absalom and Achitophel (1681): Beware the Fury of a Patient Man.
Disputed
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John C. Calhoun 15
7th Vice President of the United States 1782–1850Related quotes

“Beware the fury of a patient man.”
Pt. I, line 999–1005. Compare Publius Syrus, Maxim 289, "Furor fit læsa sæpius patientia" ("An over-taxed patience gives way to fierce anger").
Absalom and Achitophel (1681)
Variant: Beware the Fury of a Patient Man.
Context: Oh that my Pow'r to Saving were confin’d:
Why am I forc’d, like Heav’n, against my mind,
To make Examples of another Kind?
Must I at length the Sword of Justice draw?
Oh curst Effects of necessary Law!
How ill my Fear they by my Mercy scan,
Beware the Fury of a Patient Man.

God's decree on him
Ibn Shu’ba al-Harrani, Tuhaf al-'Uqul, p. 295
Religious Wisdom

“You don't knit because you are patient. You are patient because you knit.”
Things I Learned From Knitting

The Other World (1657)
Context: The most competent physician of our world advises the patient to listen to an ignorant doctor who the patient thinks is very competent rather than to a competent doctor who the patient thinks is ignorant. He reason is that our imagination works for our good health, and as long as it is supplemented by remedies, it is capable of healing us. But the most powerful remedies are too weak when the imagination does not apply them.
“Be positive, patient and persistent.”

"Rational Rationing vs. Irrational Rationing" http://www.huffingtonpost.com/jacob-m-appel/rational-rationing-vs-irr_b_622057.html, The Huffington Post (2010-06-23)