Copy paste von der Quelle unten:

Creating a Result Source to search in a list

- Go to Site Settings. Under ‘Search’, click on ‘Result Sources’.
- Click on ‘New Result Source’. Give a Name to the result source, choose the ‘Protocol’ as ‘Local SharePoint’ and ‘Type’ as ‘SharePoint Search Results’.
- Now, launch the query builder under ‘Query Transform’.
- Type the following query text:
  {SearchBoxQuery} (Path:http://[siteurl]/lists/[yourlistname]) (contentclass:STS_ListItem)

Source: http://www.manvir.net/configure-to-search-only-in-a-specific-list-or-document-library-in-sharepoint-2013/