$re = '/\d*\/\d*\/\d*, \d*:\d* - (?!\:)/m';
$str = '3/9/18, 17:47 - Pessoa 1: Oi gente!
3/10/18, 22:59 - Pessoa 2 entrou no grupo.
3/10/18, 09:35 - Pessoa 2: Salve!
O que tá rolando de bom?
3/10/18, 09:36 - Pessoa 1: Quanto tempo!';
preg_match_all($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