The Messenger of Allah ﷺ as saying: There is no alliance in Islam, and Islam strengthened the alliance made during pre-Islamic days.  

قَالَ رَسُولُ اللَّهِ ﷺ لاَ حِلْفَ فِي الإِسْلاَمِ وَأَيُّمَا حِلْفٍ كَانَ فِي الْجَاهِلِيَّةِ لَمْ يَزِدْهُ الإِسْلاَمُ إِلاَّ شِدَّةً  

The Messenger of Allah ﷺ established an alliance (of brotherhood) between the Emigrants and the Helpers in our house. He was asked: Did not the Messenger of Allah ﷺ say: There is no alliance in Islam ? He replied: The Messenger of Allah ﷺ established an alliance between the Emigrants and the Helpers in our house. This he said twice or thrice.  

سَمِعْتُ أَنَسَ بْنَ مَالِكٍ يَقُولُ حَالَفَ رَسُولُ اللَّهِ ﷺ بَيْنَ الْمُهَاجِرِينَ وَالأَنْصَارِ فِي دَارِنَا فَقِيلَ لَهُ أَلَيْسَ قَالَ رَسُولُ اللَّهِ ﷺ لاَ حِلْفَ فِي الإِسْلاَمِ فَقَالَ حَالَفَ رَسُولُ اللَّهِ ﷺ بَيْنَ الْمُهَاجِرِينَ وَالأَنْصَارِ فِي دَارِنَا مَرَّتَيْنِ أَوْ ثَلاَثًا