Authentic Supplication Number 070.

The Prophet  was such that if he entered the Masjid he would say: A`outhu bil-lahi `atheemi, wa bi-wajhihil-kareemi, wa bi-sultanihil-qadeemi min 'ash-shaytanir rajeemi (85). He said: "For when he would say that, the shaytan would say: He has been protected from me for the remainder of his day".

Footnotes.
(85) I seek protection or refuge in Allah The Magnificent, in his Noble Face, and in his ancient dominion, from the despicable shaytan".

Reporters.
Reported by Abu Dawood. Al-Albani said that its ascription was sound, that it was in his Saheeh 'Abi Dawood as #485, and that An-Nawawi, and Ibn Hajar thought it to be comely. It is #50 in The Authentic of Good Sayings.