Sahih Muslim Book 32, Hadith Number 6224.
Chapter : It is forbidden to nurse rancour.
Abu Huraim reported Allah’s Messenger (may peace be upon him) as saying The deeds of people would be presented every week on two days, viz. Monday and Thursday, and every believing servant would be granted pardon except the one in whose (heart) there is rancour against his brother and it would he said: Leave them and put them off until they are turned to reconciliation.