Wolfgang Pauli Quote
There can never be two or more equivalent electrons in an atom, for which in a strong field the values of all the quantum numbers n, k1, k2 and m are the same. If an electron is present, for which these quantum numbers (in an external field) have definite values, then this state is 'occupied.'
Quoted in M. Fierz, 'Wolfgang Pauli', in C. C. Gillispie (ed.), Dictionary of Scientific Biography (1974), Vol. 10