Related quotes
“What is life if a man cannot count on his friends when he has gone mad?”
Source: Drenai series, The King Beyond the Gate, Ch. 12

“Plato is my friend — Aristotle is my friend — but my greatest friend is truth.”
Amicus Plato — amicus Aristoteles — magis amica veritas
These are notes in Latin that Newton wrote to himself that he titled: Quaestiones Quaedam Philosophicae [Certain Philosophical Questions] (c. 1664)
Variant translations: Plato is my friend, Aristotle is my friend, but my best friend is truth.
Plato is my friend — Aristotle is my friend — truth is a greater friend.
This is a variation on a much older adage, which Roger Bacon attributed to Aristotle: Amicus Plato sed magis amica veritas. Bacon was perhaps paraphrasing a statement in the Nicomachean Ethics: Where both are friends, it is right to prefer truth.

“If the enemy of my enemy is my friend, then surely you should be friend to my friend.”
Source: The Coldest Girl in Coldtown

“My brain hums with scraps of poetry and madness.”
Source: Selected Letters

“If he is mad, so much the better; and if he is mad, I hope to God he’ll bite some of my generals.”
The New-York Magazine (November 1791) p. 662.
On being warned by the Duke of Newcastle, in 1758, against promoting James Wolfe. Often quoted as "Mad, is he? Then I hope he will bite some of my other generals."