<textarea asp-for="Body" id="Body" class="form-control" rows="10"></textarea>

<br class="p-0 m-0" />

<span asp-validation-for="Body" class="text-danger"></span>

    <script type="text/javascript">

        // replace textarea with CKEDITOR for editing data field 'Body'

        CKEDITOR.replace('Body');

        // this function make working standard jquery validation with CKEDITOR

        $(document).ready(function () {

            CKEDITOR.instances['Body'].on('key', function () {

                CKEDITOR.instances['Body'].updateElement();

                // Fire validation to update standard validation messages

                $('form').valid();

                //alert(CKEDITOR.instances["Body"].getData());

            });

        });

        // this allow you to avoid double form submission

        $('#postForm').on('submit', function () {

            for (instance in CKEDITOR.instances) {

                CKEDITOR.instances[instance].updateElement();

            }

        });

        // allow CKEDITOR to work with standard jquery validation (switch on validation for the hidden fields)

        $.validator.setDefaults({ ignore: '' });

    </script>