The Quran does NOT demand the death penalty for females who commit adultery. Instead, the punishment is either lifetime house arrest (Quran 4:15) or 100 lashes (Quran 24:2) with this verse likely abrogating the first. But Muhammad wanted death:

We read in Sahih Muslim, 17:14209: "Abu Huraira and Zaid b Khalid al-Juhani reported that one of the desert tribes came to Allah's Messenger (may peace be upon him) and said: Messenger of Allah, I beg of you in the name of Allah that you pronounce judgment about me according to the Book of Allah. The second claimant who was wiser than him said: Well, decide amongst us according to the Book of Allah, but permit me (to say something). Thereupon Allah's Messenger (may peace be upon him) said: Say. He said: My son was a servant in the house of this person and he committed adultery with his wife. I was informed that my son deserved stoning to death (as punishment for this offence). I gave one hundred goats and a slave girl as ransom for this. I asked the scholars (if this could serve as an expiation for this offence). They informed me that my son deserved one hundred lashes and exile for one year. and this woman deserved stoning (as she was married). Thereupon Allah's Messenger (may peace he upon him) said: By Him in Whose Hand is my life. I will decide between you according to the Book of Allah. The slave-girl and the goats should be given back, and your son is to be punished with one hundred lashes and exile for one year. And, O Unais (b. Zuhaq al-Aslami), go to this woman in the morning, and if she makes a confession, then stone her. He (the narrator) said: He went to her in the morning and she made a confession. And Allah's Messenger (may peace be upon him) made pronouncement about her and she was stoned to death."
The only punishments prescribed for a free female adulterer are either lifetime house-imprisonment (Quran 4:15) or 100 lashes (Quran 24:2), this second verse very likely abrogating the first. (The punishment for a slave adulterer is half of this, i.e., 50 lashes - Quran 4:25).  Nowhere in the Quran is there a command from Allah to put any adulterers to death. (Attesting to the fact that the sole punishment for a free adulterer is 100 lashes is this website's fine explanation ).   So Muhammad violated the Quran.  Now it could be argued that Allah did not reveal the commands found in Quran 4:15 and 24:2 until after the woman was killed, but that leaves us with the dilemma as to why the omniscient Allah would let the poor woman get stoned to death when he already knew that his preferred punishment for adultery is either lifetime house imprisonment or 100 lashes.  Debate Question:  Whether or not the punishment for adultery had by that time been revealed to Muhammad, why did the "compassionate and merciful" god of the Muslims fail to intervene to save the woman from a barbaric punishment?

;Muslims emulating their role model, Muhammad, and stoning adulterers to death
despite the Quran requiring a different punishment:

This lady below advocates against stoning: