$re = '/(<iframe)([\s\S]*?)(amazon.adsystem.com)([\s\S]*?)(<\/iframe>)/m';
$str = '<iframe style="width:120px;height:240px;" marginwidth="0" marginheight="0" scrolling="no" frameborder="0" src="//ws-eu.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=GB&source=ac&ref=qf_sp_asin_til&ad_type=product_link&tracking_id=keepchickens-21&marketplace=amazon®ion=GB&placement=1473689309&asins=1473689309&linkId=2ee7072c3050c40cded9c2ecdb317332&show_border=true&link_opens_in_new_window=true&price_color=333333&title_color=0066c0&bg_color=ffffff">
</iframe> some other text <iframe style="width:120px;height:240px;" marginwidth="0" marginheight="0" scrolling="no" frameborder="0" src="//ws-eu.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=GB&source=ac&ref=qf_sp_asin_til&ad_type=product_link&tracking_id=keepchickens-21&marketplace=amazon®ion=GB&placement=1473689309&asins=1473689309&linkId=2ee7072c3050c40cded9c2ecdb317332&show_border=true&link_opens_in_new_window=true&price_color=333333&title_color=0066c0&bg_color=ffffff">
</iframe> ';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php