Sahih Muslim 1805 c
According to still another version of the tradition narrated by the same authority, and handed down through a different chain of transmitters, it has been reported that they (the Companions of the Holy Prophet) were reciting rajaz verses and the Messenger of Allah (ﷺ) was (reciting) with them. And they were chanting:
O God, there is no good but the good of the Hereafter. 
So help Thou the Ansar and the Muhajirs. 
Shaiban substituted" So forgive Thou" for" So help Thou".
وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى، وَشَيْبَانُ بْنُ فَرُّوخَ، قَالَ يَحْيَى أَخْبَرَنَا وَقَالَ، شَيْبَانُ حَدَّثَنَا عَبْدُ الْوَارِثِ، عَنْ أَبِي التَّيَّاحِ، حَدَّثَنَا أَنَسُ بْنُ مَالِكٍ، قَالَ كَانُوا يَرْتَجِزُونَ وَرَسُولُ اللَّهِ صلى الله عليه وسلم مَعَهُمْ وَهُمْ يَقُولُونَ اللَّهُمَّ لاَ خَيْرَ إِلاَّ خَيْرُ الآخِرَهْ فَانْصُرِ الأَنْصَارَ وَالْمُهَاجِرَهْ وَفِي حَدِيثِ شَيْبَانَ بَدَلَ فَانْصُرْ فَاغْفِرْ ‏.‏