Commentary on Meditations: B8:49

Do not elaborate to yourself beyond what your initial impressions report. You have been told that so-and-so is maligning you. That is the report: you have not been told that you are harmed. I see that my little boy is ill. That is what I see: I do not see that he is in danger. So always stay like this within your first impressions and do not add conclusions from your own thoughts - and then that is all. Or rather you can add the conclusion of one acquainted with all that happens in the world.

This is the discipline of assent.  Practice it!  Read that first sentence again that Marcus wrote.  Someone told a rumor about you ... that is all that has happened.  You have not been harmed in this (unless you allow yourself to be harmed).  It takes practices to see things as they are without adding your opinion to the event.  Marcus says to "not add conclusions" to those events.  Practice this over and over again with everything.