Abu Huraira reported: The Prophet, peace and blessings be upon him, said:

وَالَّذِي نَفْسِي بِيَدِهِ لا تَدْخُلُوا الْجَنَّةَ حَتَّى تُسْلِمُوا وَلا تُسْلِمُوا حَتَّى تَحَابُّوا  وَأَفْشُوا السَّلامَ تَحَابُّوا وَإِيَّاكُمْ وَالْبُغْضَةَ فَإِنَّهَا هِيَ الْحَالِقَةُ لا أَقُولُ لَكُمْ تَحْلِقُ الشَّعْرَ وَلَكِنْ تَحْلِقُ الدِّينَ

By the one in whose hand is my soul, you will not enter Paradise until you submit to Allah and you will not submit until you love one another. Spread peace and you will love one another. Beware of hatred, for it is the razor. I do not say that it shaves hair, but rather it shaves away the religion.

Source: al-Adab al-Mufrad 260, Grade: Hasan