If your asylum application is finally rejected by the court, it's a normal procedure for Ausländerbehörde to request for your national passport.
This happen to all asylum seekers.
Now you only have to prove to them that you are unable to obtain your country passport with evidence .
If you fail to provide your national passport or you fail to give any tangible reasons, that might create a whole lot of problems for you in the future.
For example they can ban you from working or drastically reduce your asylum benefits. So it's in your own interests to corporate.
Note not everyone who submit his or her passport are told to leave the country, everything depends on your case at BAMF or your responsible Ausländerbehörde.