Albert Camus "is routinely categorized as an existentialist, a term he rejected on several occasions" (Wikipedia). His critique of existentialistm focused mostly on Sartre. Alain Vircondelet's biography Albert Camus, fils d'Alger (2010) mentions (on page 307) that
Il lui apparaît de plus en plus que la fameuse théorie de l'engagement dont se gargarise Sartre est une illusion, (…)
The much talked-about theory of commitment that Sartre revels in increasingly seemed an illusion to him, (…)
Is this based on an article or essay by Camus or a different type of source?