Answer:
My mother told that man was mortal.
Explanation:
In indirect speech, you make the spoken into a reported sentence, and change the verbs to past tense. You also add a descriptive verb instead of said, which conveys what the sentence wishes to convey.
It can also be written as
My mother informed that man was mortal.
My mother declared that man was mortal
Said is also fine in some cases:
My mother said that man is mortal.
Is also correct.
I hope this helps you :)