السَّلاَمُ عَلَيْكُمْ وَرَحْمَةُ اللهِ وَبَرَكَاتُهُ I was praying fajr and I thought I mispronounced the ر in a takbeer so I repeated it in the next position of salah but I repeated it from the end of the word: So I said ‘bar’ only and not ‘All?hu Akbar’ in order to repeat the raa. I think this might have been waswasah and I didn’t repeat the prayer afterwards due to thinking this. Did I commit a major sin by not praying if it was the case my prayer was invalid?

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.

It appears from your question that you have some kind of whispers, so seek refuge of Allah from them, avoid them, and do not pay any attention to them, for being carried away with them is a great evil.

With regard to what you mentioned regarding the addition of “bar” in order to pronounce the letter "ر" in a correct manner, it is one of the effects of whispers that you must avoid and ignore.

Your prayer is not invalidated by that and you did not fall into a major sin.

Allah knows best.