A Muslim can’t be taken as a slave and he can’t be executed unless he committed a crime that is punished by such.

I read Kitab Al Jihad (Ibn Nuhaas) and Yusuf Qordhowi’s Fiqh Al-Jihad. I havent found anything about war between Muslims, and there are Muslim captives. Is there any difference in ruling if the captive is Muslim? Humane treatment must be the same, but how about execution? The aforementioned books only talk about if Muslims captured a kafir, or if a Muslim soldiers was captured by the kafir, not when a Muslim soldier is captured by a Muslim.