I am a teacher at SKBZ Bangladesh islamia private...

We would like to inform you that yes, you must provide a medical certificate to prove your illness, as the Labor Law determines that the worker has the right to sick leave with pay for each year of his service. passed from the date of joining the work for the first time, provided that his illness is proven by a certificate from a doctor approved by the employer,
A worker who contracts illness after completing three months, following the probationary period, in the continuous service of an employer shall be entitled to a sick leave not exceeding 90 days, successive or otherwise, in respect of each year of service, to be calculated as follows.
• The first 15 days: with full pay.
• The next 30 days: with half pay.
• Any subsequent periods: without pay.
No wage shall be payable for sick leave if the illness is the direct result of the worker's misconduct (such as consumption of alcohol or narcotic drugs).
An employer may terminate the services of a worker who fails to report back to work after exhausting all sick leaves if the worker shall be entitled to severance pay as stipulated in this Law.