Mukhtasar Muslim

Narrated from 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. Then every servant who does not associate anything with Allah is forgiven, except for the person who harbors enmity against his brother; his forgiveness is withheld, and it is said: "Wait for these two until they reconcile. Wait for these two until they reconcile (when they reconcile, then they will be forgiven)."