His shoulders slouched, his eyes staring at

[Bassim]

I am wondering if my sentence is grammatically correct.

His shoulders slouched, his eyes staring at the wall, Peter was waiting for the doctor to tell him if was diagnosed with cancer.

 

[emsr2d2]

Remove "his eyes". You can't stare with any other part of your body. There is a word missing in the second half. Can you spot the omission? I'd change the tense at the end too.

 

[Bassim]

I will repeat my sentence with emsr2d2's corrections.

His shoulders slouched, staring at the wall, Peter was waiting for the doctor to tell him if he had been diagnosed with cancer.

 

[emsr2d2]

Now that I've read your revised version, two things occur to me:

1) You can remove "His" from the beginning too.
2) Some people might argue that the end is ambiguous. The "he" could be taken to refer to the doctor. (I think it's perfectly clear given the context.)