It’s well-known in our communities, alhamdulillah, that you can pray ‘Isha behind an imam praying Taraweeh. (Which happens if you run late, very late, indeed!) But we’re just going to dive a bit into the details of how and why this is.
Note: We do not issue fatwa! For that, please consult Islam Question and Answer!
First of all, there is a difference of opinion among the scholars about whether this is permissible or not. Let’s examine the opinion of those who say it’s not permissible (which includes the majority of companions).
What’s their proof that it’s not permissible? They cite the hadith where the Messenger of Allah (صلى الله عليه و سلم) said: “The imam was sent to be followed.” [Saheeh Bukhari, Volume 1, Book 11, #656]
How does that hadith apply? If the imam is praying Isha, you pray Isha! If he’s praying Taraweeh, you pray Taraweeh! Follow! That’s the connection.
What about the side that says that it’s permissible (and Allahu ‘alim, this side is more correct)? What’s their proof?
They cite two ahadith; one is about the companion Mu’adh (رضي الله عنه); he used to pray (a fard salaah) with the Messenger of Allah (صلى الله عليه و سلم) and then return to his people and lead them in the same prayer! [Saheeh Bukhari, Volume 1, Book 11, #668] So he might pray Dhur (for example) with the Prophet (صلى الله عليه و سلم), and then go back to his city/tribe/etc. and lead them in Dhur.
The other proof is salaat-ul-khawf, the fear prayer; when praying in a state of fear (i.e. on the battlefield), you only pray two rakaahs. Once, the Messenger of Allah (صلى الله عليه و سلم) prayed two rakaahs of salaat-ul-khawf with one group of companions, and stood up and prayed another two rakaahs of salaat-ul-khawf with a different group of companions. (The second time it was nafl for him (صلى الله عليه و سلم), but fard for those companions behind him.)
Notice, this is exactly the same situation as praying Isha when the imam prays Taraweeh–imam praying nafl, and you praying fard.
But what about the hadith that the imam was sent to be followed? How does this group view it? They say that it means, as the hadith says, the imam should be physically followed; make rukoo’ when he makes rukoo’, sujood when he makes sujood, etc. Abdul-Bary Yahya, in the Purification Act fiqh of salaah class, also confirms this understanding, and mentions an example: if the imam intended his prayer to be riyaa (i.e. showing off, i.e. minor SHIRK) would this hadith command you to have that intention? No! So the hadith means physically follow the imam.
Wallahu ta’ala ‘alim. (You can also pray Isha when the imam prays Witr, according to the same understanding.)
For the full story, read the Islam QA Fatwa on this topic.
“Praying ‘Isha’ behind someone who is praying Taraweeh or Witr.” Islam Question and Answer. 2 Sept. 2008 <http://islamqa.com/en/ref/79136>.
Abdul-Bary Yahya. Lecture. AlMaghrib. The Purification Act. University of Toronto, Toronto. November 2006.