one of my friend came to dubai after received a...

In case your inquiry related to the arrival of one of your friends to the Emirates according to a visa and the employer refuses to stamp the visa, here is the following information:
If the employer refuses to stamp your friend's visa, your friend can file a complaint against the employer, provided that the complaint is submitted to:
-Ministry of Human Resources and Emiratisation.
- General administration of residence.
It remains to point finally ...
According to the UAE labor law, the employer has the right to terminate the contract of employment during the probationary period without warning the worker or paying the end of service gratuity.
Here is the text of the UAE Labor Law related to your inquiry:
Article 37
A worker may be employed on probation for a period not exceeding six months, during which the employer without notice or severance pay may terminate his services. A worker shall not be placed on probation more than once with the same employer. Where a worker successfully completes the period of probation and continues in employment, the said period shall be calculated as part of his period of service.