Disable hyphenation for an entire paragraph

You can set \hyphenpenalty=10000 and \exhyphenpenalty=10000, so TeX sees hyphens as “infinitely bad” and avoids them. Add \sloppy if you want to make TeX obey margins at all costs, adding extra inter word spaces to preserve the margins justification.

You can have an environment to do that for you:

\documentclass[12pt,a5paper]{article}

\usepackage{lipsum}

\newenvironment{nohyphens}{%
  \par
  \hyphenpenalty=10000
  \exhyphenpenalty=10000
  \sloppy % Makes TeX obey margins by stretching inter word spaces
}{\par}

\begin{document}

\lipsum[2]

\begin{nohyphens}
\lipsum[2]
\end{nohyphens}

\end{document}

You can use the nil language from babel:

\documentclass[]{article}
\usepackage[nil,ngerman]{babel}

\textwidth=3cm
\begin{document}
deutscher Textabschnitt mit Trennungen

{\selectlanguage{nil}%
deutscher Textabschnitt mit Trennungen\par
}


\end{document}