Missing endcsname inserted error

I have the following latex code which produces the error mentioned in the title:

documentclass{article}
%usepackage{flexisym}
%usepackage[T1]{fontenc}
%usepackage{array}
usepackage{setspace}
usepackage{amsmath}


begin{document}
numberwithin{
[ 
left( begin{array}{c}
textrm{$;dtextprime;$}\
textrm{$;stextprime;$}\
textrm{$;btextprime;$}
end{array} right)

]
}
end{document}

If I remove the numberwithin command and add the flexisym package but remove the amsmath package, it runs fine. Also, if I remove the numberwithin command and add the flexisym package and amsmath package, I get an error saying,”amsmath.sty: Latex error or: command dfrac already defined”. Can someone please point out the mistake due to which I get these errors? I somehow need the numberwithin command to be working with arrays.