There is a hadith regarding someone being victim of waswasa, and the Prophet advising him to say "a'udhu billahi min ash-shaytani-r-rajim" and to "spit" thrice on his left.

But - having discussed this on a thread on our forum - it's not clear if this refers to doing that during the Salah or outside it for other kind of waswasah.

I have the doubt that doing that during the Salah may actually invalid it?

Anyone could help?..