labour under a delusion BrE
labor under a delusion AmE

Can you genuinely tell me, without a bit of scientific evidence either way, that you are right, and that I am wrong - and worse, labouring under a delusion?

I cannot even allow myself to see you laboring under a delusion which a word from me can remove.

"Are we laboring under a delusion of free will?

His tone suggested that, whatever it might be, Duke Brown was undoubtedly laboring under a delusion.

Thraxton was just as sure he labored under a delusion, but what point to tell a blockhead that he was a blockhead?

I consider it strange that any person should labor under a delusion and yet be aware that it was a delusion: in fact, if he were aware of his state, which could be no delusion.'"