Praise be to Allah, and may Allah’s peace and blessings be upon the Messenger of Allah, his family and his companions.
As to what follows:
With regards to answering your question we say, success is by Allah Almighty.
The scholars have two views regarding this:
First: if he goes down to sit then Prayer will be invalid. This is the view held by Shafites and Ahmad in one narration.
Second: if he goes down to sit before reciting, Prayer will not be invalid. This is the famous view held by Ahmad.
The first view is the correct view if the person is an Alim, but if he is uneducated or has forgotten his Prayer will be correct.
And Allah knows best.
Your brother,
Dr. Khalid al-Muslih
18 / 12 / 1429 AH