Hadith: The blood of a Muslim is inviolable except by one of three

عَنِ ابنِ مَسعُودٍ رَضِيَ اللَّهُ عَنْهُ قَالَ: قَالَ رَسُولُ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ:
«لَا يَحِلُّ دَمُ امْرِئٍ مُسْلِمٍ إِلَّا بِإِحْدَى ثَلَاثٍ: الثَّيِّبُ الزَّانِي، وَالنَّفْسُ بِالنَّفْسِ، وَالتَّارِكُ لِدِينِهِ المُفَارِقُ لِلْجَمَاعَةِ».
[صحيح] - [متفق عليه] - [صحيح مسلم: 1676]

Ibn Mas‘ūd (may Allah be pleased with him) reported: The Messenger of Allah (ﷺ) said:
"The blood of a Muslim is inviolable except by one of three: adultery of a married person, a life for a life (homicide), and abandoning Islam and separating from the Islamic body.''
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Muslim - 1676]

Explanation

The Prophet (ﷺ) clarified that a Muslim is inviolable unless he commits one of the three: First: He who commits adultery after being legally married, it is lawful that he be stoned to death. Second: He who intentionally kills an inviolable person unlawfully is killed with the relevant conditions. Third: He who separates from the Islamic body, either by leaving his religion of Islam altogether by apostatizing, or departs from it by abandoning part of it, without apostasy, like those who engage in transgression, highway robbery, and rebels such as the Kharijites and others.

Benefits from the Hadith

1. It is prohibited to do any of these three things. He who commits any of them deserves the death penalty, either for Kufr (disbelief), which applies to apostates from Islam, or as a legal punishment, which applies in the cases of a married adulterer and an intentional murderer.
2. It is obligatory to safeguard our honor and keep it untainted.
3. The Hadīth indicates that it is obligatory to respect Muslims and that their blood is inviolable.
4. We are urged to stick to the Muslim community and not to separate from it.
5. The excellence of the Prophet's method of teaching (ﷺ) as his speech is sometimes divided into points, such that the issues are listed and combined. This is quicker to memorize.
6. Allah legislated legal punishments to deter criminals, protect society, and preserve it from crimes.
7. Implementation of the legal punishments lies within the authority of the ruler.
8. The causes that warrant killing are more than three, but they do not fall outside these categories. Ibn al-‘Arabi al-Māliki said: They never go beyond these three under any circumstance; for whoever practices sorcery or insults a Prophet of Allah has committed disbelief, and thus falls under the category of the one who has abandoned his religion.