diff --git a/rails/test-out-url-and-path-helpers-in-the-console.md b/rails/test-out-url-and-path-helpers-in-the-console.md
index 1923c39..744f2d7 100644
--- a/rails/test-out-url-and-path-helpers-in-the-console.md
+++ b/rails/test-out-url-and-path-helpers-in-the-console.md
@@ -36,3 +36,5 @@ and `*_url` path helpers.
 
 For the `*_url` path helpers, make sure you have [`default_url_options`
 set](set-default-url-options-for-entire-application.md).
+
+[source](https://stackoverflow.com/a/13553422/535590)