\documentclass[a4paper,11pt,msc]{SBU}
\input{commands}
\usepackage{stmaryrd}
\usepackage{amssymb,amsmath,amsthm}
\usepackage{float}
\usepackage[]{natbib}
\begin{document}


سلام
\cite{kumar2000hardness}
\bibliographystyle{plain}%{chicago-fa}
\setLTRbibitems
\resetlatinfont 
\bibliography{ref}
\end{document}