An official ID....my wife is German and has a personalauweise / identity card plus she has a passport, either will suffice as a form of identity.
I am British and we don't have Identity cards. Just passports which our ultimate form of ID and travel document.
My wife can travel in and out of Schengen with either passport or ID, I can travel with my passport only, in order for it not to be stamped I need to produce my residency card to prove I am exempt from the stamp.
When you leave or enter Schengen you must produce your residency card to ensure you don't get a stamp, then all will be well.
I am British and we don't have Identity cards. Just passports which our ultimate form of ID and travel document.
My wife can travel in and out of Schengen with either passport or ID, I can travel with my passport only, in order for it not to be stamped I need to produce my residency card to prove I am exempt from the stamp.
When you leave or enter Schengen you must produce your residency card to ensure you don't get a stamp, then all will be well.