Back when ISIS was still expanding into the multi-ethnic and religiously diverse northern Iraq, not just Yazidis but also the country's 1 million Christians were some of their main targets. They were asked to either convert or leave, otherwise they would be killed. All along, churches were being bombed or burnt to the ground.
Most of the Christians that used to inhabit those areas of the Levant where ISIS now rules have been displaced, in an act of religious/ethnic cleansing more thorough than any that Saddam had ever achieved. And ISIS is still working through the backlog of churches to be destroyed. Only recently they destroyed one that was described as equivalent to Canterbury Cathedral.
Muslim scholars I have spoken to have stated that such actions are completely un-Islamic, strictly against Sharia and a blasphemy against the Prophet Muhammad more serious than any they can think of from history. The Qur'an commands Muslims to follow Muhammad and his example:
"O you who believe! Obey God and obey the Messenger" (4:59)
This and dozens of other verses in the Qur'an compel Muslims to obey Muhammad. And this is why Sharia law is based not just on the Qur'an, but also on the Sunnah, the words, the life and the practices of the Prophet.
And the Prophet Mohammad was very clear about how Muslims should treat Christians. He entered a treaty with them which deserves to be quoted in full here:
This is a message from Muhammad ibn Abdullah, as a covenant to those who adopt Christianity, near and far, we are with them.
Verily I, the servants, the helpers, and my followers defend them, because Christians are my citizens; and by Allah! I hold out against anything that displeases them.
No compulsion is to be on them. Neither are their judges to be removed from their jobs nor their monks from their monasteries. No one is to destroy a house of their religion, to damage it, or to carry anything from it to the Muslims' houses.
Should anyone take any of these, he would spoil God's covenant and disobey His Prophet. Verily, they are my allies and have my secure charter against all that they hate.
No one is to force them to travel or to oblige them to fight. The Muslims are to fight for them. If a female Christian is married to a Muslim, it is not to take place without her approval. She is not to be prevented from visiting her church to pray. Their churches are to be respected. They are neither to be prevented from repairing them nor the sacredness of their covenants.
No one of the nation (Muslims) is to disobey the covenant till the Last Day (end of the world).
("Covenant of the Prophet Muhammad with the Monks of Mount Sinai", CE 628)
These words were written in a Patent given by the Prophet Muhammad in Medina to a delegation of Christian monks from St. Catherine's Monastery at Mount Sinai. The Patent was signed with the Prophetic seal.
The original has since been moved from St. Catherine's monastery by Sultan Selim I of the Ottoman Empire in 1517, and today can be seen in the Topkapi Museum in Istanbul. When he took the document from the monastery, the Sultan and Caliph of Islam Selim renewed its terms and gave the resident monks a copy.
The Prophet granted unconditional protection and what today we would recognise as basic human rights to Christians, near and far. All true Caliphs since then have observed this treaty, as they have been compelled to do till the Last Day (IE this treat can not be abrogated). There are few things in the Sharia that can be as clear as this prescription towards Christians.
But today, Wahhabi clerics and ISIS fanatics seem to think that they know better than the Prophet himself how to be good Muslims. And that now includes destroying all churches, in direct violation of God's covenant.
Wahhabis say they want to emulate the life and times of the Prophet. ISIS and their "Caliph" want to rebuild the original Caliphate to represent the entire ummah. So why are their teachings and their actions then exactly opposed to those of the very first Islamic state of Muhammad in Medina (CE 622)?
The Prophet's Constitution of Medina brought together what Muslim scholars describe as an ummah wahidah where all the residents of the state, Muslims, Jews, Christians and pagans, ensured religious freedom, gave all groups representation, established the security of women and declared that no weapon can be carried or blood be spilled on the haram land of the Islamic state.
Has there ever been a group of people to call themselves "Muslim", while they spit on the Prophet's treaties written on paper, they dishonour his law and precedent, and with the most breath-taking arrogance claim that they know better how to be good Muslims by calling itself a "Caliphate"? Has there ever been any group of people in the world that has blasphemed so obscenely against God's covenant and God's Prophet before?
Dr Azeem Ibrahim is an International Security Lecturer at the University of Chicago and Adj Research Professor at the Strategic Studies Institute US Army War College