$re = '/[\wа-я]* (?:(?:[а-я]\w)|(?:\w[а-я])) [\wа-я]*/xm';
$str = 'aaa
bbb
a1c
zzяяzzяя qwe1фasd фывйфыф1
п1п
wwя
я12
яяя
1я
1яa';
preg_match_all($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