
\documentclass{article}
\usepackage{fontspec}
\setmainfont{Libertinus Serif}
\pagestyle{empty}
\directlua{
fonts.handlers.otf.addfeature {
    name = "smcp",
    type = "multiple",
    data = {
            ['ḥ'] = { "h.sc", 0x0323 },
 	    ['ā'] = { "a.sc", 0x0304 }, 
    },
  }
}

\begin{document}
\textsc{Aḥmad b. Fażlān b. al-ʿAbbās b. Rašīd}
\end{document}
