Question Summary:
Nafl Salah after witr

Question Detail:

Is the 2 rakaat nafl at the end of isha, sunnat to pray sitting down?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
The Prophet (Sallallahu Alaihi Wa Sallam) used to sit and perform the two raka’as nafl salah after the witr salah.[1]
In principle, if one sits and performs nafl salah, he will get half the reward of standing and performing nafl salah. Some Ulama prefer sitting down and performing the salah in spite of getting half the reward as that was the habit of Rasoolullah (Sallallahu Alaihi Wa Sallam).[2]
And Allah Ta’āla Knows Best
Zakariya Memon
Student Darul Iftaa
Chatham, Canada 
Checked and Approved by,
Mufti Ebrahim Desai.
Daruliftaa.net