You must give a reason for suspending a user

app/assets/javascripts/admin/controllers/admin_suspend_user_controller.js

@@ -9,8 +9,13 @@
 **/
 Discourse.AdminSuspendUserController = Discourse.ObjectController.extend(Discourse.ModalFunctionality, {
 
+  submitDisabled: function() {
+    return (!this.get('reason') || this.get('reason').length < 1);
+  }.property('reason'),
+
   actions: {
     suspend: function() {
+      if (this.get('submitDisabled')) return;
       var duration = parseInt(this.get('duration'), 10);
       if (duration > 0) {
         var self = this;

app/assets/javascripts/admin/templates/modal/admin_suspend_user.js.handlebars

@@ -10,6 +10,6 @@
   </form>
 </div>
 <div class="modal-footer">
-  <button class='btn btn-danger' {{action suspend}}><i class='fa fa-ban'></i>{{i18n admin.user.suspend}}</button>
+  <button class='btn btn-danger' {{action suspend}} {{bind-attr disabled="submitDisabled"}}><i class='fa fa-ban'></i>{{i18n admin.user.suspend}}</button>
   <a {{action closeModal}}>{{i18n cancel}}</a>
 </div>