KORAN:

047.004
YUSUFALI: Therefore, when ye meet the Unbelievers (in fight), smite at their necks; At length, when ye have thoroughly subdued them, bind a bond firmly (on them): thereafter (is the time for) either generosity or ransom: Until the war lays down its burdens. Thus (are ye commanded): but if it had been Allah's Will, He could certainly have exacted retribution from them (Himself); but (He lets you fight) in order to test you, some with others. But those who are slain in the Way of Allah,- He will never let their deeds be lost.

“As for the captives, the amir [ruler] has the choice of taking the most beneficial action of four possibilities: the first to put them to death by cutting their necks; the second, to enslave them and apply the laws of slavery regarding their sale and manumission; the third, to ransom them in exchange for goods or prisoners; and fourth, to show favor to them and pardon them. Allah, may he be exalted, says, 'When you encounter those [infidels] who deny [the Truth=Islam] then strike [their] necks' (Qur'an sura 47, verse 4)”....Abu’l-Hasan al-Mawardi, al-Ahkam as-Sultaniyyah." [The Laws of Islamic Governance, trans. by Dr. Asadullah Yate, (London), Ta-Ha Publishers Ltd., 1996, p. 192. Emphasis added.]

"Those who were brought in alive [having surrendered] were ordered beheaded, after which a tower of skulls was erected in the camp." [The Baburnama -Memoirs of Babur, Prince and Emperor, translated and edited by Wheeler M. Thacktson, Oxford University Press,1996, p. 188. Emphasis added.]