How to disable the single view for a custom post type?

METHOD 1:

Redirect to a custom URL for single view, archive page is still publicly accessible.

You can use template_redirect hook to redirect for a custom post type, you can use any other URL you want to in place of home_url() and the error code in other argument.

<?php
add_action( 'template_redirect', 'wpse_128636_redirect_post' );

function wpse_128636_redirect_post() {
  if ( is_singular( 'sample_post_type' ) ) {
    wp_redirect( home_url(), 301 );
    exit;
  }
}
?>

METHOD 2:

Completely disable Single or Archive page from front-end; Works for a Custom post only.

A alternative approach is to specify value for param publicly_queryable while registering the custom post if you are ok with displaying a 404 page. [ Thanks @gustavo ]

'publicly_queryable'  => false

It hides single as well as archive page for the CPT, basically completely hidden from front-end but can be done for custom posts only.

This second solution is best suitable for the scenario where you need a Custom post for admin/back-end usage only.