Update: More details emerging; apparently it's not as easy as 'quote a Koranic passage':
Now if it happens that you are taken prisoner by somebody, and they just happen to ask you to recite the Shahada (but remember nobody has ever done anything because of religion, it's just a coincidence), call their bluff and recite it!
I can't tell if you need to ululate at the end or not.
Kassim Traoré, a Malian journalist who was in a building about 50 metres from the Radisson, said the attackers had told hostages to recite a declaration of Muslim faith as a way separating Muslims from non-Muslims.
Those who could recite the declaration, the Shahada, were allowed to leave the hotel. The al-Shabab, an al-Qaeda affiliate in East Africa, used a similar approach in the attack at the Westgate Mall in Nairobi in 2013.
Now if it happens that you are taken prisoner by somebody, and they just happen to ask you to recite the Shahada (but remember nobody has ever done anything because of religion, it's just a coincidence), call their bluff and recite it!
Shahada said:There is no god but God. Muhammad is the messenger of God.
I can't tell if you need to ululate at the end or not.