Protection of life, wealth and honor
On the occasion of the Farewell Hajj, the Holy Prophet (Sallallahu alaihi wa sallam) said:
فَإِنَّ دِمَاءَكُمْ وَأَمْوَالَكُمْ وَأَعْرَاضَكُمْ بَيْنَكُمْ حَرَامٌ كَحُرْمَةِ يَوْمِكُمْ هَذَا فِى بَلَدِكُمْ هَذَا
Translation: Indeed! Your life, wealth and honor are sacred among you the way this day of yours is distinguished and sacred.
Islam has declared every man’s life, wealth and honor as sacred. Murdering someone has been declared a great sin so much so that murder of one person has been declared tantamount to killing off all humankind. Almighty Allah says in the Holy Quran:
كَتَبْنَا عَلَى بَنِي إِسْرَائِيلَ أَنَّهُ مَن قَتَلَ نَفْسًا بِغَيْرِ نَفْسٍ أَوْ فَسَادٍ فِي الْأَرْضِ فَكَأَنَّمَا قَتَلَ النَّاسَ جَمِيعًا وَمَنْ أَحْيَاهَا فَكَأَنَّمَا أَحْيَا النَّاسَ جَمِيعًا
We prescribed (this commandment in the Torah sent down) to the Children of Israel that whoever killed a person (unjustly), except as a punishment for murder or for (spreading) disorder in the land, it would be as if he killed all the people (of society); and whoever (saved him from unjust murder and) made him survive, it would be as if he saved the lives of all the people (of society, i.e., he rescued the collective system of human life).
The second interpretation is that if a person makes so bold so as to kill a fellow human being, then that person will not hesitate to wipe out all humankind if he/she gets to lay hands on such resources, say like nuclear bombs.
In the same way, saving somebody is akin to saving all humankind.
The Holy Prophet (Sallallahu alaihi wa sallam) has declared:
وَالْمُؤْمِنُ مَنْ أَمِنَهُ النَّاسُ عَلَى دِمَائِهِمْ وَأَمْوَالِهِمْ
Translation: A believer is one from whom other people are assured of the safety of their lives and wealth.