Source

File: wp-includes/ms-functions.php

function wpmu_create_user( $user_name, $password, $email ) {
	$user_name = preg_replace( '/\s+/', '', sanitize_user( $user_name, true ) );

	$user_id = wp_create_user( $user_name, $password, $email );
	if ( is_wp_error( $user_id ) ) {
		return false;
	}

	// Newly created users have no roles or caps until they are added to a blog.
	delete_user_option( $user_id, 'capabilities' );
	delete_user_option( $user_id, 'user_level' );

	/**
	 * Fires immediately after a new user is created.
	 *
	 * @since MU (3.0.0)
	 *
	 * @param int $user_id User ID.
	 */
	do_action( 'wpmu_new_user', $user_id );

	return $user_id;
}