Anas ibn Malik reported that the Messenger of Allaah (peace be upon him) said:
"Do not bear grudges against one another, envy one another, or boycott one another, but rather be brothers, servants of Allaah. Indeed it is unlawful for a Muslim to dissociate himself from his Muslim brother for more than three days." [Saheeh al-Bukhaaree & Saheeh Muslim]