The ruling on making up a missed rak'ah in congregation

The questioner:
What should I do if I missed a rak'ah with the congregation while they were occupied with an image, the 'Asr prayer, and the fire of the night, and I have an extra rak'ah?

The Shaykh:
Do not believe in sustenance.

The questioner:
And I am standing in a rak'ah. Do not say "sitting."

The Shaykh:
Sit down when the imam says the taslim, then make up your rak'ah with him. Sit down, and you are the one they know has an extra rak'ah, so they do not stand up. When he says the taslim, you stand up and make up your rak'ah; you do not stand up [with them].

The questioner:
Is this equal [rak'ah] considered?

The Shaykh:
Do not stand up with him; alert him, but do not stand up with him. When he says the taslim, you stand up and make up the rak'ah.

The questioner:
Even if he prayed four rak'ahs due to the imam's forgetfulness.

The Shaykh:
It is not counted; the making up is done after the taslim. Yes.