الكافي 2/1/75/15

15. A number of our people have narrated from Ahmad ibn Muhammad from Ali ibn al-Hakam from abu al-Maghra’ from Abu ‘Abdillah عليه السلام who has said the following: “The Muslim is the brother of the Muslim (in belief). He does not do injustice to him, does not betray him, and does not violate his trust. It is worthwhile for the Muslims to be assiduous in maintaining good relations with each other, be kind to each other, assist the needy ones financially and be compassionate toward each other so that they can be as Allah, the Most Majestic, the Most Holy, has commanded them to be, ‘Compassionate toward each other, ’ (48:29) kind to one another and feel sad for their absence from them. You should be just as the group of Ansar (the supporters) was in the lifetime of the Messenger of Allah عليه السلام as mentioned in (48:29) .’”