I have a question about Namaz.
We pray and praise Almighty Allah in our Namaz because he is our lord. Why do we add praise for prophet saws in our Namaz. With all respect to prophet saws, but we pray praise and prostrate to Allah.
And as Allah mentions in the last verse of Surah Isra as well to praise him in our namaz.

And secondly, was the Namaz during prophets time the same as we do it now? Did he praise himself as well in the namaz?

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We are not praising prophet in the prayers. We are asking Almighty to praise him, and this is a recommended thing, not part of the prayers. You can leave it, except in tashahud, where it is mandatory.
Yes. Prophet used to say it in his prayers in tashahud. This is agreed by all Muslims.