Full Idea
Every theorem of mathematics has a counterpart with set theory - ...but that theory cannot serve as a basis for the notion of proof.
Gist of Idea
Set theory will found all of mathematics - except for the notion of proof
Source
Shaughan Lavine (Understanding the Infinite [1994], V.3)
Book Reference
Lavine,Shaughan: 'Understanding the Infinite' [Harvard 1994], p.133