$re = '/^VIR\s+RECU\s+(\d+)\nDE:\s+([\s\S]*?)(\nMOTIF:\s+(.*))?$/';
$str = 'VIR RECU 998721687978
DE: Mrs PAUL SMITH
564
MOTIF: ANY REASON';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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