It is a letter written by a student to class teacher or principal.
From
To
Respected sir/madam,
As my cousin has met with an accident and is admitted in emergency ward, My parents have to stay with my cousin during his hospitalization and attend to his needs. So, I could not attend my classes for the next two days. I request you to consider my absence as leave for these two days only (from __ to __).
Thanking you.
Yours sincerely,
___________