All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Jalsatul-Istiraahah (sitting for a while after making two prostrations and before moving to the standing position) is desirable according to the most correct opinion. Some scholars are of the opinion that it is not desirable. However, we do not know of any scholar who considers the Jalsatul-Istiraahah to be an obligatory act.
Allah knows best.