Full Idea
It may perhaps be granted that every grammatically well-formed expression representing a proper name always has a sense. But this is not to say that to this sense there also corresponds a reference.
Gist of Idea
Every descriptive name has a sense, but may not have a reference
Source
Gottlob Frege (On Sense and Reference [1892]), quoted by Bernard Linsky - Quantification and Descriptions 3.1
Book Reference
'Bloomsbury Companion to Philosophical Logic', ed/tr. Horsten,L/Pettigrew,R [Bloomsbury 2014], p.91
A Reaction
Presumably this concerns fictional names such as 'Pegasus'. It seems to be good simple evidence for the distinction between sense and reference.