Is it permissible for a mujahid to combine prayers when he is neither traveling nor a displaced person?

The question requires clarification of the circumstances of the mujahid (fighter). If he is in a state of war, the Fear Prayer (Salat al-Khawf) and combining prayers are legislated for him. However, if he has no excuse such as fear, illness, or rain, then combining prayers is not permissible for him.