Labelling Multi-"node" Path

I would like to ask for a path drawn with the following command

\draw [->] (4) to [out=225,in=0] (11) to [out=180,in=-90] (12) to [out=90] (2);

How can I add a sloped label to the path. Furthermore, if I would like the label appear on the section between (12) and (2), what should I do?

Thanks!

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Edited

My apologies. The code and generated output is as below.

\begin{tikzpicture}[->,>=stealth',node distance=5cm,font=\small\setstretch{1.0}]

    \node [state] (1) [] {A};
    \node [state] (2) [below=15cm of 1] {B};
    \node [state] (3) [left of=2] {C};
    \node [state] (4) [above of=3] {D};
    \node []      (5) [below=1cm of 3] {};
    \node []      (6) [left  of=4]  {};

    \draw [->,smooth] (2) to [out=225,in=0] (5) to [out=180,in=-90] (6) to [out=90] (1);

\end{tikzpicture}