Full Idea
Soundness is normally a matter of having true axioms and a truth-preserving proof system.
Gist of Idea
Soundness is true axioms and a truth-preserving proof system
Source
Peter Smith (Intro to Gödel's Theorems [2007], 03.4)
Book Reference
Smith,Peter: 'An Introduction to Gödel's Theorems' [CUP 2007], p.24
A Reaction
The only exception I can think of is if a theory consisted of nothing but the axioms.