Fix a typo [ci skip]
diff --git a/user_guide_src/source/libraries/form_validation.rst b/user_guide_src/source/libraries/form_validation.rst
index 14305b6..22272dc 100644
--- a/user_guide_src/source/libraries/form_validation.rst
+++ b/user_guide_src/source/libraries/form_validation.rst
@@ -399,7 +399,7 @@
functions. This permits you to extend the validation class to meet your
needs. For example, if you need to run a database query to see if the
user is choosing a unique username, you can create a callback function
-that does that. Let's create a example of this.
+that does that. Let's create an example of this.
In your controller, change the "username" rule to this::