Authentic Supplication Number 144.

`Uthman bin 'Abil `As said: I said: O' Messenger of Allah! The shaytan came as a screen between me, my prayer, and my recitation causing me confusion in it ? So he  said: "That is a shaytan called Khanzab, so if you sense him then seek refuge in Allah from him, and spit to your left three times." So I did that, and Allah made him go away from me.

Reported by Muslim, and is #110 in The Authentic of Good Sayings.