Riyad us Saliheen: Hadith 1592

The Messenger of Allah (ﷺ) said, "People's deeds are presented before Allah on Mondays and Thursdays, and then every slave (of Allah) is granted forgiveness (of minor sins) if he does not associate anything with Allah in worship. But the person in whose heart there is rancour against his brother, will not be pardoned. With regard to them, it is said twice: 'Hold these two until they are reconciled'."

[Muslim].