Sahih Muslim
The Book of Jihad and Expedition (Kitab Al-Jihad wal-Siyar)
Book Number: 019 / Hadith Number: 4448
It has been narrated (through a still difterent chain of transmitters) by Anas that the Companions of Muhammad (may peace be upon him) were chanting on the day of the Battle of the Ditch:
We are those who have sworn allegiance to Muhammad
(And made a covenant with him) to follow Islam as long as we live.
Hammad is not sure whether Anas said:" Ala'l-Islam" or," Ala'l-Jihad". And the Holy Prophet (may peace be upon him) was chanting:
O God, the real good is the good of the Hereafter,
So forgive Thou the Ansar and the Muhajirs.