diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 1c5a737696edadbbde20ecdb4535150ba647aefe..e73b855241af8bd76b1228d258d153bf30858891 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -1366,6 +1366,17 @@ def has_one(name, scope = nil, options = {})
# * Post#create_author! (similar to post.author = Author.new; post.author.save!; post.author)
# The declaration can also include an +options+ hash to specialize the behavior of the association.
#
+ # === Scopes
+ #
+ # You can pass a second argument +scope+ as a callable (i.e. proc or
+ # lambda) to retrieve a specific record or customize the generated query
+ # when you access the associated object.
+ #
+ # Scope examples:
+ # belongs_to :user, -> { where(id: 2) }
+ # belongs_to :user, -> { joins(:friends) }
+ # belongs_to :level, ->(level) { where("game_level > ?", level.current) }
+ #
# === Options
#
# [:class_name]