Dear Alex,
The text that you have given is suitable for general notice and not for addressing to specific to an employee. The warning letter can go like this:
To,
Mr/Ms __________
Employee No: -
________________ (name of company)
________________ (name of city)
Sleeping while on Duty
1. While on duty on _______ (date), you were found sleeping at _______ (place), at _______ hours (time).
2. Sleeping on duty constitutes the misconduct under the following clause of Standing Orders applicable to you:
" ____________ "
3. You are hereby warned to be careful of your conduct while on duty. Recurrence of this misconduct or any other misconduct will lead to initiation of severe disciplinary action against you.
For _____________ (name of the company)
_____________ (name of the issuing authority)
_____________ (designation of the issuing authority)