Manual:$wgRedirectSources

Interwiki links and sites: $wgRedirectSources
Regular expression to restrict URLs which will be displayed as "redirected from" links.
Introduced in version:1.5.0
Removed in version:Still in use
Allowed values:(regular expression) or false
Default value:false

Details

Other wikis which set $wgDisableHardRedirects to false may redirect users to pages of your wiki, telling your MediaWiki install from what URL they came from. Set this regular expression to restrict origin URLs which will be displayed as "redirected from" links to them.

It might look something like this:

$wgRedirectSources = '!^https?://[a-z-]+\.wikipedia\.org/!';

(For instance, this example configuration is pointless because Wikipedia doesn't have hard redirects enabled.)

Leave as false to avoid displaying any incoming redirect markers. This does not affect intra-wiki redirects, which don't change the URL.