Full Idea
For Nietzsche, the true belief is the one which augments one's power.
Gist of Idea
True beliefs are those which augment one's power
Source
report of Friedrich Nietzsche (The Will to Power (notebooks) [1888]) by Roger Scruton - Short History of Modern Philosophy Ch.13
Book Reference
Scruton,Roger: 'A Short History of Modern Philosophy' [ARK 1985], p.193
A Reaction
Scruton probably had in mind Idea 4534, from The Will to Power, but wider reading suggests this is not Nietzsche's view of truth, which was much more robust. Nietzsche was obsessed with identifying the motivation for a love of truth.
Related Idea
Idea 4534 'Truth' is the will to be master over the multiplicity of sensations [Nietzsche]