It is narrated from Sayyiduna Abu Huraira (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) said: "The gates of Paradise are opened on Mondays and Thursdays, and every servant who does not associate anything with Allah is forgiven, except the person who harbors enmity against his brother. It is said regarding these two people: 'Wait for these two until they reconcile, wait for these two until they reconcile.'" (That is, until they make peace with each other, they are not forgiven.)