“I have always been a pencil.”

Source: Speak, Memory

Quote from Constable's letter to Rev. John Fisher (22 July 1812), as quoted in Richard Friedenthal, Letters of the great artists – from Blake to Pollock (Thames and Hudson, London, 1963), p. 40
1800s - 1810s

Letter to his literary agent, found on his desk after his death in 1968
Writers at Work (1977)

version in original Dutch / origineel citaat van Suze Robertson: Nee, ik ben volstrekt nooit wat men noemt een begaafd kind geweest, nooit een droomster. Aan fantasie met 't potlood op 't papier dacht ik niet, al leerden we op school natuurlijk ook teekenen en muziek. Maar in dien tijd was de piano eigenlijk meer mijn fort.. .Toch heb ik tot mijn achttiende jaar tussen die beide lang gewankeld.
Source: 1900 - 1922, Onder de Menschen: Suze Robertson' (1912), p. 30

On Alan Lee
In the Artist's Studio interview (2010)
Context: From Alan, I learned to take a more instinctive and intuitive approach to pencil work. I used to let my mind get far too far ahead of my pencil, which can be productive, but removes the serendipitous switch of direction when the pencil and hand discover an idea the mind’s eye had missed. Drawing at the right speed is a sort of graphic contrapposto providing what I’d be tempted to call an “intuitional resilience” unobtainable with more energetic methods. I very much enjoyed working with him, a situation of symbiosis between enthusiasm and despair, the former because his work is just so good, the latter because his work is just so good. He is hard to keep up with, but then I believe he says the same of me. He is a dear friend and a wonderful artist.

Letter #158 to Theo (24 September 1880) http://www.vangoghletters.org/vg/letters/let158/letter.html <!-- This letter has slightly different translations everywhere, but this seems to be the more often quoted translation -->
Variant translation http://www.webexhibits.org/vangogh/letter/8/136.htm: "I felt my energy revive and I said to myself, I shall get over it somehow, I shall set to work again with my pencil, which I had cast aside in my deep dejection, and I shall draw again, and from that moment I have had the feeling that everything has changed for me"
1880s, 1880
Context: I felt my energy revive, and said to myself, In spite of everything I shall rise again: I will take up my pencil, which I have forsaken in my great discouragement, and I will go on with my drawing. From that moment everything has seemed transformed for me.

God doesn't believe in atheists (2002)

Source: Zen and the Art of Motorcycle Maintenance: An Inquiry Into Values