That quote comes from part II of a great two-part interview that Pat Butcher conducted with Ed Whitlock.
Part I:
http://www.globerunner.org/01/extraordinary-mr-whitlock/
and
Part II:
http://www.globerunner.org/01/infamous-mr-whitlock/
Whitlock reveals the importance of time off as it admits he's taken more than a year off continuously in the last decade to get healthy.