\documentclass[10pt,a4paper]{article}
\usepackage{arabtex}
\newcommand{\mamouni}{
\begin{Large}
\begin{arabtex}
mamwonI mowlAI asmaA-`Il
\end{arabtex}
\end{Large}
}
\begin{document}

\begin{center}
\textbf{Niveau Avancé} 

\textbf{TP 4 : Texte en arabe sous \LaTeX}  
\end{center}

\begin{flushleft}
\mamouni
\end{flushleft}

\begin{arabtex}
bismi al-llahi al-rra.hmani al-rra.hImi
\\
\\
\hspace{20mm}wa `al_A al-llahi falyatawakkali al-mutawakkilUn
\begin{flushleft}
.sadaqa al-llahu al-`a.zIm
\end{flushleft}
\end{arabtex}


\end{document}