Ajax呼叫设置错误。

Here is a loop in my code in which i send ajax call to some API to fetch data. it works fine for first iteration(outer loop), but show error on 2nd and onward . here is code:

$.ajaxSetup({ cache: true, jsonpCallback: 'quranData' }); // define ajax setup

for (var counter = 1; counter < 4; counter++) //outer loop
{
    $.getJSON("http://api.globalquran.com/surah/"+counter+"/quran-simple?jsoncallback=?", {
        format: "jsonp"
    }, function (Obj) {
        $.each(Obj.quran, function (i, by) {
            $.each(by, function (verseNo, line) {
                var obj = {
                    'ayah_no': line.ayah_no,
                    'ayah': line.ayah,
                    'surah': line.surah,
                    'verse': line.verse
                };
                c++;
                num++;
                things.push(obj);
            });
        });
    });
} //outer loop ends

Error:

> Uncaught TypeError: Property 'quranData' of object [object Object] is not a function 

this happens only when i run outer loop, how to fix it ?