how can prevent change text on PageLenght Button?

hi

i use this code for my pageLenght button

    buttons: [
        {
            text:       '<i class="fa fa-list"></i>',
            titleAttr:  'page lenght',
            extend:     'pageLength',
        }]

and my page lenght button have an icon (not a text)
but when i click on sub buttons (for example 10 rows) page lenght icon changed to "10 rows"

how can i prevent change text on Page Lenght Button???