How to check only one argument in a unit test in c#, when a multiargument method is called?

Question

I am writing a unit test for a method. In this method a method of the EventsApi with a similar signature is called:

Task<EventCollection?> GetEvents(DateTime? createdFrom = null, DateTime? createdTo = null, string? source = null, string? type = null);

And I would like to make sure, that the method is called with a specified source. How to do it, what to put here?

eventsApi.Verify(x => x.GetEvents(<what_to_put_here?>));