$re = '/\b(\d{10}) {6}\t(\d{10})\b(?=[\s\S]*\b\1 {6}\t\2)\b/m';
$str = '+----------------+---------------+------------+
| Reference Date | Instrument ID | Entity ID |
+----------------+---------------+------------+
| 2019-06-28 4251675720 1000183742 |
+----------------+---------------+------------+
| 2019-06-28 4251675720 1000183742 |
+----------------+---------------+------------+
| 2019-06-28 2113750655 100065856 |
+----------------+---------------+------------+
| 2019-06-28 3512075270 1002923999 |
+----------------+---------------+------------+
| 2019-06-28 4251998103 1003890261 |
+----------------+---------------+------------+
| 2019-06-28 4239113350 1004043945 |
+----------------+---------------+------------+
| 2019-06-28 8569030255 1004043945 |
+----------------+---------------+------------+
| 2019-06-28 6692802619 1004584989 |
+----------------+---------------+------------+
| 2019-06-28 6751615521 1005048991 |
+----------------+---------------+------------+
| 2019-06-28 1338818134 1005076529 |
+----------------+---------------+------------+
| 2019-06-28 1903780287 1005519781 |
+----------------+---------------+------------+
| 2019-06-28 3023132803 1005535434 |
+----------------+---------------+------------+
| 2019-06-28 3075990149 1006443568 |
+----------------+---------------+------------+
| 2019-06-28 1821112520 1007165898 |
+----------------+---------------+------------+
| 2019-06-28 4249904989 100753094 |
+----------------+---------------+------------+
| 2019-06-28 4230960972 1009300504 |
+----------------+---------------+------------+
| 2019-06-28 2254190165 1010611747 |
+----------------+---------------+------------+
';
preg_match_all($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