The Metaphysics of Morals by Immanuel Kant Chapter 2 Page 15

their physic right strong, they spoil it. For the commonest understanding shows that if we imagine, on the one hand, an act of honesty done with steadfast mind, apart from every view to advantage of any kind in this world or another, and even under the greatest temptations of necessity or allurement, and, on the other hand, a similar act which was affected, in however low a degree, by a foreign motive, the former leaves far behind and eclipses the second; it elevates the soul and inspires the wish to be able to act in like manner oneself.

Even moderately young children feel this impression, and one should never represent duties to them in any other light.

From what has been said, it is clear that all moral conceptions have their seat and origin completely a priori in the reason, and