https://tex.stackexchange.com/q/433066/35864 - test in an empty directory to make sure the .bib file is created

ascite.tex

\documentclass{article}

\usepackage[numbers]{natbib}
%\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@book{AS,
  editor    = {Milton Abramowitz and Irene Stegun},
  title     = {Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables},
  year      = {1970},
  publisher = {Dover},
  address   = {New York},
}
\end{filecontents}

\begin{document}
\citet[section 4.6]{AS}

\bibliographystyle{plainnat}
\bibliography{\jobname}
\end{document}