Question Summary:
when must inniwajato be read when one is performing sallat in jamaat

Question Detail:

when must inniwajato be read when one is performing sallat in jamaat

Answer :

In the name of Allah, Most Gracious, Most Merciful
Assalaamu `alaykum waRahmatullahi Wabarakatuh
 Our illustrious jurists mention that a person should recite
 
إني وجهت وجهي للذي فطر السماوات والأرض حنيفا وما أنا من المشركين (الانعام 79)
I have, indeed, turned my face straight towards the One who created the heavens and the earth, and I am not one of those who associate partners with Allah. [6:79]
 
before one could make his intention for salah. Some scholars give permission to recite it after reciting  thana in nafl salah only.
 
لكن في الحلية: الحق أن قراءته قبل النية أو بعدها قبل التكبير لم تثبت عن النبي (ص) ولا عن أصحابه ا ه.
وفي الخزائن: وما ورد محمول على النافلة بعد الثناء في الاصح ا ه.
 حاشية رد المحتار - (ج 1 / ص 488)
 الفتاوى المحمودية 5/577
And Allah knows best
Wassalam
Ml. Ishaq E. Moosa,
Student Darul Iftaa
Checked and Approved by:
Mufti Ebrahim Desai
Darul Iftaa, Madrassah In'aamiyyah