In other places, for example: "Causal inference in statistics: An overview", which is in effect the Cliff Notes version of his book, he writes:

"one cannot substantiate causal claims from associations alone, even at the population level -- behind every causal conclusion there must lie some causal assumption that is not testable in observational studies."

Here is a similar survey article from 2003, in which he writes that exact sentence, followed by:

"Nancy Cartwright (1989) expressed this principle as "no causes in, no causes out", meaning that we cannot convert statistical knowledge into causal knowledge."

Interesting, but how do those files evade word searches for the parts you've quoted?