In his will, Imam Ali (AS) said:

You are advised/recommended to join together and unite, and forgive each other. Never abandon each other and do not break the bonds of friendship and do not destroy relationship/connection with each other; otherwise your bad ones will dominate you. Then, Allah (SWT) will not respond to your requests (prayers) [1].

[1] Nahjul Balaghah, Letter 47.

Source: en.shafaqna.com