Sahih Muslim 1805 d
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:
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.
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 ‏"‏ ‏.‏