How to connect filebeat to azure elasticsearch

what will be the elastic search ip/url of azure elastic-search as it contains 3 master node and 3 slave node.

Are you talking about the Elasticsearch Service?

yes , which is deployed on azure.

On this page you can see the example MyDeployment - Configure Beats and Logstash with Cloud ID | Elasticsearch Service Documentation | Elastic
You will want to click the Copy endpoint link for Elasticsearch.