One day Abba Isaac went to a monastery. He saw a brother committing a sin and he condemned him.

  When he returned to the desert, an angel of the Lord came and stood in front of the door of his cell, and said, "I will not let you enter."  But he persisted saying, "What is the matter?"  And the angel replied, "God has sent me to ask you where you want to throw the guilty brother whom you have condemned."  Immediately he repented and said, "I have sinned, forgive me."  Then the angel said, "Get up, God has forgiven you. But from now on, be careful not to judge someone before God has done so."