How to add a featured image from a URL in WordPress

add-featured-image-from-url.php

<?php
//----------------------------------------------------------------------
// Step 1: Create a Post Dynamically
//----------------------------------------------------------------------
// Register Post Data
$post = array();
$post['post_status']   = 'publish';
$post['post_type']     = 'post'; // can be a CPT too
$post['post_title']    = 'My New Post';
$post['post_content']  = 'My new post content';
$post['post_author']   = 1;

// Create Post
$post_id = wp_insert_post( $post );

// set featured image from extranal image
set_featured_image_from_external_url( 'http://s.wordpress.org/style/images/wp-header-logo.png', $post_id );

media-handle-sideload.php

<?php
//----------------------------------------------------------------------
// Method 1: Upload image form extranal url via WP media_handle_sideload
// @return ID
//----------------------------------------------------------------------
function upload_image_from_external_url_media_handle_sideload($image_url = NULL){
	
	if ( ! filter_var($image_url, FILTER_VALIDATE_URL) ) {
		return;
	}
	
	// Need to require these files
	if ( !function_exists('media_handle_upload') ) {
		require_once(ABSPATH . "wp-admin" . '/includes/image.php');
		require_once(ABSPATH . "wp-admin" . '/includes/file.php');
		require_once(ABSPATH . "wp-admin" . '/includes/media.php');
	}
	
	// Add Featured Image to Post
	$url = preg_replace('/\?.*/', '', $image_url); // removing query string from url & Define the image URL here
	$tmp = download_url( $url );
	if( is_wp_error( $tmp ) ){
		// download failed, handle error
		return;
	}
	
	$pathinfo = pathinfo($url);
	
	/**
	 * now we can actually use media_handle_sideload
	 * we pass it the file array of the file to handle
	 * and the post id of the post to attach it to
	 * $post_id can be set to '0' to not attach it to any particular post
	 */
	$post_id = 0;
	$desc = $pathinfo['filename'];
	$file_array = array();

	// Set variables for storage
	// fix file filename for query strings
	preg_match('/[^\?]+\.(jpg|jpe|jpeg|gif|png)/i', $url, $matches);
	$file_array['name'] = basename($matches[0]);
	$file_array['tmp_name'] = $tmp;

	// If error storing temporarily, unlink
	if ( is_wp_error( $tmp ) ) {
		@unlink($file_array['tmp_name']);
		$file_array['tmp_name'] = '';
	}

	// do the validation and storage stuff
	$id = media_handle_sideload( $file_array, $post_id, $desc );

	// If error storing permanently, unlink
	if ( is_wp_error($id) ) {
		@unlink($file_array['tmp_name']);
		return $id;
	}else{
		return $id;
	}

	$src = wp_get_attachment_url( $id );
}

//----------------------------------------------------------------------
// set the featured image from extranal url
//----------------------------------------------------------------------
$attachment_id = upload_image_from_external_url_media_handle_sideload('https://s.w.org/about/images/logos/wordpress-logo-stacked-rgb.png');
if( $attachment_id ){
	set_post_thumbnail( $post_id, $attachment_id ); // set featured image via $post_id and $attach_id 
}

set-featured-image-from-external-url.php

<?php
//----------------------------------------------------------------------
// Method 2: set the featured image from extranal url
//----------------------------------------------------------------------
function set_featured_image_from_external_url($url, $post_id){
	
	if ( ! filter_var($url, FILTER_VALIDATE_URL) ||  empty($post_id) ) {
		return;
	}
	
	// Add Featured Image to Post
	$image_url 		  = preg_replace('/\?.*/', '', $url); // removing query string from url & Define the image URL here
	$image_name       = basename($image_url);
	$upload_dir       = wp_upload_dir(); // Set upload folder
	$image_data       = file_get_contents($url); // Get image data
	$unique_file_name = wp_unique_filename( $upload_dir['path'], $image_name ); // Generate unique name
	$filename         = basename( $unique_file_name ); // Create image file name

	// Check folder permission and define file location
	if( wp_mkdir_p( $upload_dir['path'] ) ) {
		$file = $upload_dir['path'] . '/' . $filename;
	} else {
		$file = $upload_dir['basedir'] . '/' . $filename;
	}

	// Create the image  file on the server
	file_put_contents( $file, $image_data );

	// Check image file type
	$wp_filetype = wp_check_filetype( $filename, null );

	// Set attachment data
	$attachment = array(
		'post_mime_type' => $wp_filetype['type'],
		'post_title'     => sanitize_file_name( $filename ),
		'post_content'   => '',
		'post_status'    => 'inherit'
	);

	// Create the attachment
	$attach_id = wp_insert_attachment( $attachment, $file, $post_id );

	// Include image.php
	require_once(ABSPATH . 'wp-admin/includes/image.php');

	// Define attachment metadata
	$attach_data = wp_generate_attachment_metadata( $attach_id, $file );

	// Assign metadata to attachment
	wp_update_attachment_metadata( $attach_id, $attach_data );

	// And finally assign featured image to post
	set_post_thumbnail( $post_id, $attach_id );
}
//----------------------------------------------------------------------
// set the featured image from extranal url
//----------------------------------------------------------------------
set_featured_image_from_external_url('https://s.w.org/about/images/logos/wordpress-logo-stacked-rgb.png', $post_id);

Your article is fabulous. but I have some issues, sir I don't want to upload image. I want to use external URL as feature image. basically I want use feed to publish article but I cant upload another website image and use my own URL .
I want use feature image from another website URL and when open post it redirect another website article.