As for the issue of burning:

Indeed, When a group of men from the companions of ‘Abdullah bin Saba’ Al-Humairi (عبد الله بن سبأ الحميري) – may Allah curse him – came to ‘Ali bin Abi Talib – may Allah be pleased with him – and one of them said to him : “You are him” he asked : “And who is ‘him’!” And the man responded: “You are Allah” – ‘Ali – may Allah be pleased with him – denounced it severely and saw it as something big, and he ordered to ignite a fire and he burnt them with the fire. And he – may Allah be pleased with him – used to say regarding this :

When I saw the matter to be evil I ignited a fire and called Qanbar

Qanbar is one of his servants and he is the one who was appointed to throw these people into the fire [Al-Milal wa An-Nihal , Ah-Shahrustani]

So this is the rightly guided Khalifa – may Allah be pleased with him – burning people with fire.

Ibn Kathir mentions in his history book (Al-Bidayah wa An-Nihayah) that : (Khalid called Malik bin Nuweera [مالك بن نويرة] and impressed upon Malik [the evil of] what has happened from him by following Sajah, and denying to give Zakah and he said : Do you not know that it is the companion of Salah?

Malik responded: Surely your companion used to claim that.

So [Khalid] said : Is he our companion and not your companion? O Dhirar! Strike his neck! So his head was struck off. It was ordered to bring the head and to put the head with two rocks and a pot cooked on these Khalid ate from it that night, to terrorize the apostates from the Bedouins and others besides them.

And it is said that the hair of Malik made the fire go on even till the meat inside the pot cooked well, and the hair was not burnt fully due to its abundance.

Abu Qatadah talked with Khalid over what he did and they differed in the matter. So Abu Qatadah went to [Abu Bakr] As-Sihdeeq and complained about him. And ‘Umar talked to Abu Qatadah regarding Khalid and said to As-Sihdeeq : Dismiss him for surely in his sword is a madness. [ dismiss from the role of commander]

So Abu Bakr said : “I will not sheathe a sword that Allah has unsheathed upon the disbelievers …” [Al-Bidayah wa An-Nihayah : 6/355]

‘Umar – may Allah be pleased with him – after dismissing Khalid and seeing what he did to the enemies with his battalion that was preceding the army of Abu ‘Ubaida in Sham – he said : “May Allah have mercy on Abu Bakr, He was more knowledgeable of people compared to me.”

The sword of Allah – Abu Sulayman [Khalid bin Waleed] – may Allah be pleased with him was a professor in the art of Islamic Terrorism and a valuable school after the prophet – peace and blessings be upon him. And in terrorizing he has influence and excursions that narrates his strange expertise and his fine knowledge in the different methods of psychological warfare.

And he – may Allah be pleased with him – said during the Battle of Ullais, like it has been narrated in “Al-Bidayah wa An-Nihaya” : – “ O’ Allah, if you give us their shoulders [give us victory over them], it is obligatory on me upon you that I will not leave anyone amongst them whom I able to overpower, till I make their river flow with their blood”. Thereafter Allah gave them their shoulders [i.e. enabled to overpower them and take them captive], whence the announcer of Khalid called out “Capture, capture and do not kill them except those who refrain from being captured”. So the cavalrymen conceded with them in droves forcefully driving them. And Khalid appointed men who were ordered to strike the necks of the captives at the river. This was carried out for a day and night and the same was sought from them for a further two consecutive days. And everytime one of those captives was brought his neck was struck at the river, but the water of the river had moved on. So some of his commanders said : Indeed the river will not flow with their blood till you send the water upon the blood and then it will flow with it, enabling you to fulfill your promise, so he sent the water [i.e. there was a dam which prevented the water flow] and so the river flowed fresh blood and due to that the river was called the river of blood even to this day. And the windmill cycled that water which was mixed with fresh blood which sufficed the army for three complete days. And the number of those killed reached seventy thousand…)

The battle “Ullais” was the one and the same after which the Righteous Caliph Abu Bakr As-Sihdeeq – may Allah have mercy on him – said : (O’ people of Quraysh, your lion has surely hastened upon the lion and won over its flesh. Women have become incapable of giving birth to the likes of Khalid bin Al-Waleed)

And from the result of Khalids terrorizing was that “Al-Akyadir” (الأكيدر) the ruler of Dumat al-Jundal said to his people : (I am the most knowledgeable of people regarding Khalid, no one has had an auspicious omen made compared to him in battle and there is no one shaper than him, And no people has ever seen the face of Khalid whether they were few or numerous except they got defeated at it, so obey me and make peace with the people.)

As for the books of Fiqh (jurisprudence) and Hadith, they mention the issue of burning disbelievers in the Books of Jihad and Battle. It has come in “Nayl Al-Awtaar” written by Ash-Shawkani [Chapter in leaving off making an example out of [enemies] and burning and cutting down trees, and breaking down buildings except for a need or benefit] while explaining a hadith narrated by Abu Huraira wherein he said : (Allah’s Messenger – peace and blessings be upon him – sent us on an expedition and said : If you find so-and-so and so-and-so, burn the two of them with fire, thereafter when we were about to depart he said: “I have indeed ordered you to burn so-and-so and so-and-so, but indeed the fire, is not punished by it except from Allah, so if you find them both, kill them) [Narrated by Ahmad, Al-Bukhari, Abu Dawud and Tirmidi]

Ash-Shawkani – may Allah have mercy on him – said : (His saying “And indeed the fire, it is not punished by it except from Allah” is a news which means by it forbiddance. However the predecessors have differed as to verdict of burning. ‘Umar, ibn Abbas and others besides them both disliked it absolutely whether it was due disbelief or in a state of fighting or in Qisas (retribution) whereas ‘Ali and Khalid bin Al-Waleed and others besides them both permitted it.)

And in the book of Hudud (prescribed punishments) in “Nayl Al-Awtar” it is mentioned : (Al-Bayhaqi also extracted from Abu Bakr that he convened with the people regarding a man who used to be married like women are married off (that is indulge in homosexuality), so he asked the companions of the messenger of Allah – peace and blessings be upon him and upon his family – regarding that. And that day, the most severe of them in statement was ‘Ali bin Abi Talib – peace be upon him – who said : “This is a sin which no nation from the nations disobeyed with except one. You all are aware of what Allah did to them. I am of the view that we should burn him with fire” – so the companions of the messenger of Allah – peace and blessings be upon him and his family – agreed upon burning him with fire. So Abu Bakr wrote to Khalid bin Al-Waleed commanding him to burn the man with fire.)

Ash-Shawkani said : (And in its chain of narration is an Irsal – (original narrator not mentioned) but it has been narrated with another chain from Ja’far bin Muhammad from his father who narrated from ‘Ali – in this story it is said : Stone and Burn with fire.)

Isn’t there in his statement : (so the companions of the messenger of Allah – peace and blessings be upon him and his family – agreed upon burning him with fire) evidence which shows that there is no presence of Ijma’ (consensus) regarding the impermissibility of burning!

And it has also come in “Nayl Al-Awtar”, narration from Al-Mundhiri : (The Lootiyya (sodomites) were burnt with fire by Abu Bakr, ‘Ali, ‘Abdullah bin Az-Zubayr and Hisham bin Abdul Malik.)

And it has also been mentioned in “Fath Al-Bari” that Al-Mihlab said : (This forbidding is not to say it is impermissible (haram), but rather due to humbleness. The evidence for permissibility of burning is shown by the actions of the Sahabah. The prophet – peace and blessings be upon him – has gorged out the eyes of the people of “Al-‘Urniyyeen” (العرنيين) with heated iron. And Abu Bakr burnt the aggressors with fire in the presence of the Sahabah, Khalid bin Al-Waleed burnt people from the people of Ridda (apostasy), and the majority of the scholars of Medina allow burning down forts and carriages (boats etc) upon the people inside them as mentioned by An-Nawawi and Al-Awza’ee)

And in “ ‘Awn Al-Ma’bood” Al-Qustulany (القسطلاني) mentions : (The predecessors have differed regarding burning. ‘Umar, ibn Abbas and others besides them both disliked it absolutely whether it was for the reason of disbelief or retribution. Whereas ‘Ali and Khalid bin Al-Waleed allowed it.)

This mater is an issue which has been differed in it by the Sahabah and the predecessors of the Ummah. The truthful of this Ummah has done it, and the righteous caliph ‘Ali bin Abi Talib has done so, and so has a group of the Sahabah, so there is no Ijma’ (consensus) in the matter like some claim…