How to encode JSON embedded within JSON

I have a JSON string and one of the fields is a text field. This text field can contain text that a user enters in the UI and if the text they enter is JSON text, perhaps to illustrate some coding, I need to encode their text so that it does not get interpreted as JSON within the actual JSON structure sent to the server.

When the JSON structure is received by the server and gets decoded, I need to make sure the embedded JSON gets decoded as text, which ends up looking like JSON in the UI.

In effect, how do you escape an embedded JSON string?