@Jakub_Sypianski this is not possible with our tool at the moment, so it would have to be done manually. As suggested in this article from our Help Center, you could accumulate “ancient text” references in another document and add that bibliography manually once you’ve finished citing.
You could also use the Cite feature available from the library (e.g. grouping references in a folder and using the top menu option or Ctrl+C to obtain formatted citations), or even BibGuru (our free citation generator) to the same end.
Although not currently in our plans, this feature has been requested before (here and here) so it’s on our radar. Adding your +1 to the topic on our internal tracker.