Form Validation: Let the comma as separator to be valid in integer field input
If you have integer (or Big int) field you can't submit data with , in integer field and this means that you should strip all , before data passed to Drupal default form submit handler ( as you know before data passed to submit it must be  validated first ) So  the tiny and quick solution is  you set a custom  validate handler  that  called before Drupal node validation handler then in there try to strip all , ( manipulate data in your custom validation handler ) and then enjoy it.

 // in your custom module 

function yourmodule_form_alter(&amp;$form, &amp;$form_state, $form_id)
{
    if ($form_id == 'your_form_id' ) {
                array_unshift($form['#validate'], '_mycustom_validate_handler');
}
}

function _mycustom_validate_handler($form, &amp;$form_state)
{
$form_state['values']['your_integer_field']['und'][0]['value'] =strtr($form_state['values']['your_integer_field']['und'][0]['value'] , ',' ,'');
}


And if you also  want save , in database(!!!) try text field instead using integer field  and then with client side validation  Regex  Rule validate what you want.