How do I get an array of repeated characters from a string using LINQ?

string s = "abcdefghab";

s.ToCharArray().OrderBy(a => a)...

String text = "dssdfsfadafdsaf";
var repeatedChars = text.ToCharArray().GroupBy(x => x).Where(y => y.Count() > 1).Select(z=>z.Key);

string theString = "abcdefghab";

//C# query syntax
var qry = (from c in theString.ToCharArray()
           group c by c into g
           where g.Count() > 1
           select g.Key);

//C# pure methods syntax
var qry2 = theString.ToCharArray()
            .GroupBy(c => c)
            .Where(g => g.Count() > 1)
            .Select(g => g.Key);

var qry = (from c in theString
           group c by c into g
           where g.Count() > 1
           select g.Key);