# Numbering only the last equation in a set of equations

I have the following long equation:

\begin{align}
F\bigl(\mathbf{u};z \;\vert\; Z(\mathbf{u}') \leq z'\bigr)
&= \prob\bigl\{ Z(\textbf{u}) \leq z,Z(\mathbf{u}') \leq z'\bigr\} \\
&= \dfrac{\prob \bigl\{Z(\mathbf{u}) \leq z,Z(\mathbf{u}') \leq z'\bigr\}}
{\prob \bigl\{Z(\mathbf{u}') \leq z'\bigr\}} \\
&= \dfrac{F(\mathbf{u},\mathbf{u}';z,z')}
{F(\mathbf{u}';z')}
\end{align}


It looks like this for now:

But, I would like to number once i.e. something like this:

I have many questions that are connected to each other so have to mention them throughout my writing..

Any suggestions will be greatly appreciated.

For those parts of the equation you don't want to number, add \nonumber:

\documentclass{article}

\usepackage{amsmath}
\DeclareMathOperator{\prob}{Prob}

\begin{document}

\begin{align}
F\bigl(\mathbf{u};z \mid Z(\mathbf{u}') \leq z'\bigr)
&= \prob\bigl\{ Z(\mathbf{u}) \leq z \mid Z(\mathbf{u}') \leq z'\bigr\} \nonumber \\
&= \dfrac{\prob \bigl\{Z(\mathbf{u}) \leq z,Z(\mathbf{u}') \leq z'\bigr\}}
{\prob \bigl\{Z(\mathbf{u}') \leq z'\bigr\}} \nonumber \\
&= \dfrac{F(\mathbf{u},\mathbf{u}';z,z')}
{F(\mathbf{u}';z')}
\end{align}

\end{document}