Do not hire a man who does your work for money, but him who does it for love of it.
It is remarkable that there are few men so well employed, so much to their minds, but that a little money or fame would commonly buy them off from their present pursuit.
 Henry David Thoreau, Life Without Principle (1863). copy citation

Context

“and, even in a pecuniary sense, it would be economy for a town to pay its laborers so well that they would not feel that they were working for low ends, as for a livelihood merely, but for scientific, or even moral ends. Do not hire a man who does your work for money, but him who does it for love of it. It is remarkable that there are few men so well employed, so much to their minds, but that a little money or fame would commonly buy them off from their present pursuit. I see advertisements for active young men, as if activity were the whole of a young man's capital. Yet I have been surprised when one has with confidence proposed to me, a grown man, to embark in some enterprise of his, as if I had absolutely nothing to do, my life having been a complete failure hitherto.” source