Authentic Supplication Number 138.

It is reported of the Prophet  that he used to say upon confronting the enemy: 'Allahumma 'anta `adhudee, wa 'anta naseeree, bika 'ahoolu, wa bika 'asoolu, wa bika 'uqatilu (158).

Footnotes.
(158) O' my 'ilah You are my upper-arm, and You are my triumpher. By You I move, and by You I assault, and by You I fight.

Reporters.
Al-Albani said that it was reported by Abu Dawood in al-jihad with sound ascription by way of Qatadata by way of 'Anas. He also said that Ibn Hibban (#1661) said it was sound. Al-Albani included this hadeeth in The Authentic of Good Sayings as #104.