Diagnosed with dengue - HR is threatening him that they can fire/terminate him

One of my friend got diagnosed with dengue before perhaps 1.5 month and came back to work after 10 days and he was working for 3-4 days and again diagnosed with malaria so this time he decided not to come back until he fell well & it's took him 1 month.
He submitted all the medical report for first 10 days leave when he got diagnosed with dengue.
But the second time he admitted into government hospital so doctor gave him only 5 days rest certificate. This time he took leave for 1 month but he has medical proof only for 15 days. He don't have anything for another 15 days.
HR asked to make fake report and submit but he don't want to cheat them.
Hr is threatening him that they can fire/terminate him.
Is it legal this type of situation for HR or Employer? Is there any law that help him?

But the second time he admitted into government hospital so doctor gave him only 5 days rest certificate. - If doctor was sure that he can be recovered in 05 days only then why he took more unauthorized leave by Taking Employer Granted?
This time he took leave for 1 month but he has medical proof only for 15 days. He don't have anything for another 15 days - Again why he took more Unauthorized Leaves?

Dear Amar,
Ask your friend to use good mosquito repellent and HR is asking for certificate to validate that he had medical condition he doesn't seem to care about its legitimacy. Please request him to consider your leave with out certificate and don't repeat such mistake in the future.

Dear Colleague,
In my view HR is acting unprofessional and putting undue pressure .It is outright illegal.
The matter deserves to be escalated to higher ups by proper representation.
At the cost of being blunt, if any body deserves to be fired it is HR person.
Regards,
Vinayak Nagarkar
HR- Consultant