Dear ZEE here is a sample,
Date:
To whom it may concern
I hereby certify that Mr................. of ............. nationality, Holding passport No. ...... worked as ..................... for ...................... company from ............. to ...................... With a total monthly salary of ....................... for .......... working hours per week.
During his work with the company his main duties and responsibilities were:
A...........................
B...........................
C............................
Signed by direct supervisor
Stamped by company's official seal ( If Applicable )