This plugin will add the favicon of the domain to which your URL is pointing.
This is the simplest way, no need for hidden codes or any other modifications.
Just download and enable the plugin and all the links from your posts and pages will display the favicon of the domain to which they are pointing.
Your own internal links will not be affected.
You don’t have to do anything just install the Faviconized Links plugin and add links to your post and pages normally:
Waiting your feedback,open towards improvements and innovations.