nameserver - DNS - how does it resolve the name servers itself?

Domain name: abc.com
Name Server: ns1.abc.com and ns2.abc.com

I am running a DNS server and hosting the zone (abc.com) on-premise.

When a client wants to resolve *.abc.com, it will query ns1.abc.com or ns2.abc.com, that is straight forward.

The question is how does it resolve ns1.abc.com before it can sends query to it?