Do soldiers sin if they carry out a flawed order from the commander in battle? Do they have to offer expiation for that, and why did Khalid ibn al-Walid, Usama ibn Zayd, and the Khawarij not pay blood money for those they killed by mistake?

The scholars have agreed on the obligation to obey the ruler in matters that are not sinful. The subjects are obliged to offer him advice with gentleness, wisdom, and good admonition if he makes a non-fundamental error that does not affect the core principles of Sharia. If he does not heed the advice, then patience becomes obligatory.

However, it is not permissible to obey him when a sin that contradicts the definitive and established teachings of Islam becomes apparent. If the ruler's error and his transgression against Allah's command become evident, then it is not permissible to follow him. Nevertheless, he bears no sin if the origin of this error was due to a permissible ijtihad (independent reasoning).

In the case of accidental killing by a mujtahid (the Imam or his deputy), there is no sin upon him, and the blood money (diyah) is to be paid from the public treasury (Bayt al-Mal). This is the view of Al-Thawri, Abu Hanifa, Ahmad, and Ishaq. Alternatively, it is to be paid by the ruler's 'aqila (kinsmen responsible for paying blood money), which is the view of Al-Awza'i, Abu Yusuf, Muhammad, and Al-Shafi'i.