Sahih al-Bukhari, Volume 9, Book 83, Hadith 3 (USC-MSA) ⓘ
Narrated `Abdullah bin `Umar: One of the evil deeds with bad consequence from which there is no escape for the one who is involved in it is to kill someone unlawfully.
حَدَّثَنِي أَحْمَدُ بْنُ يَعْقُوبَ، حَدَّثَنَا إِسْحَاقُ، سَمِعْتُ أَبِي يُحَدِّثُ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، قَالَ إِنَّ مِنْ وَرْطَاتِ الأُمُورِ الَّتِي لاَ مَخْرَجَ لِمَنْ أَوْقَعَ نَفْسَهُ فِيهَا، سَفْكَ الدَّمِ الْحَرَامِ بِغَيْرِ حِلِّهِ.
also referenced under: Book 87, Hadith 3 (In-Book) & Hadith 6863 (DarusSalam)