Must one fast two months along with paying diyah in the event of a rocket, prepared and launched by a mujahid, striking another mujahid, thereby mistakenly killing a Muslim? And upon whom is the fasting incumbent?

If a Muslim is killed by mistake in battle by a mujahid, then his blood money is to be paid by the Muslim treasury (Bayt al-Mal), as in the story of Al-Yaman. And expiation (freeing a slave or fasting two consecutive months) is obligatory upon the one who launched the missile, because he is the direct perpetrator. Indemnity falls upon the direct perpetrator when a cause and a direct act combine.