Respected Sir/Madam,
I am _______(name), working as __________ (designation) having my employee ID number ________ (employee ID number).
I write this email most humbly to request you for sanctioning sick leave under my name, as I am suffering from back pain/ backache for last _________ (number of days) days. The doctor has advised me to take rest. I would request you to kindly sanction me sick leave so that I will be able to have rest. If you need to contact me regarding this matter, you can reach me at ________ (contact details).
I believe that you would consider approving the leave at the earliest. I shall be highly obliged.
Thanking you,
Sincerely,
__________ (Name),
__________ (Employee ID number)