Full Idea
Arithmetic forms its own concepts of numbers by successive addition of units in time.
Gist of Idea
Numbers are formed by addition of units in time
Source
Immanuel Kant (Prolegomena to Any Future Metaphysic [1781], 284)
Book Reference
Kant,Immanuel: 'Prolegomena to Any Future Metaphysic', ed/tr. Lucas,Peter G. [Manchester UP 1971], p.39
A Reaction
It is hard to imagine any modern philosopher of mathematics embracing this idea. It sounds as if Kant thinks counting is the foundation of arithmetic, which I quite like.