How do you write a letter on leave you have already taken?

Date

To whom it may concern:

This is to document the reason for my absence (on ...) (from ... to ...) due to (illness, brief description) (an accident, brief description) (a family emergency, it's not necessary to describe family personal business) (a death in the family, etc.).

I was unable to contact (you, the office, the manager, etc.) to advise of my absence at the time due to the (day, time of day, etc.). I had asked (name or relationship of person asked) to contact (the appropriate person or place) to advise of my absence when there would be someone available to take the message.

Sincerely,