Sahih Muslim 1805
Sahih Muslim · Book 32: The Book of Jihad and Expeditions · The Battle of Al-Ahzab (The Confederates), also known as Al-Khandaq (The Ditch)
It has been narrated (through a still difterent chain of transmitters) by Anas that the Companions of Muhammad (ﷺ) were chanting on the day of the Battle of the Ditch:
حَدَّثَنِي مُحَمَّدُ بْنُ حَاتِمٍ ، حَدَّثَنَا بَهْزٌ ، حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ ، حَدَّثَنَا ثَابِتٌ ، عَنْ أَنَسٍ ، أَنَّ أَصْحَابَ، مُحَمَّدٍ صلى الله عليه وسلم كَانُوا يَقُولُونَ يَوْمَ الْخَنْدَقِ نَحْنُ الَّذِينَ بَايَعُوا مُحَمَّدًا عَلَى الإِسْلاَمِ مَا بَقِينَا أَبَدًا أَوْ قَالَ عَلَى الْجِهَادِ . شَكَّ حَمَّادٌ وَالنَّبِيُّ صلى الله عليه وسلم يَقُولُ " اللَّهُمَّ إِنَّ الْخَيْرَ خَيْرُ الآخِرَهْ فَاغْفِرْ لِلأَنْصَارِ وَالْمُهَاجِرَهْ " .
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 Prophet (ﷺ) was chanting: O God, the real good is the good of the Hereafter, So forgive Thou the Ansar and the Muhajirs.