from his father, from his grandfather that the Prophet (ﷺ) said: "Whoever kills [a believer] deliberately, he is handed over to the guardians of the one killed. If they wish to, they have him killed, and if they wish to, they take the blood-money. That is thirty Hiqqah, thirty Jadha'ahs and forty pregnant camels. Whatever (amount more) they require from him, than that is for them (if they choose)." THat is because of the severity of blood-money.
حَدَّثَنَا أَحْمَدُ بْنُ سَعِيدٍ الدَّارِمِيُّ، أَخْبَرَنَا حَبَّانُ، وَهُوَ ابْنُ هِلاَلٍ حَدَّثَنَا مُحَمَّدُ بْنُ رَاشِدٍ، أَخْبَرَنَا سُلَيْمَانُ بْنُ مُوسَى، عَنْ عَمْرِو بْنِ شُعَيْبٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ مَنْ قَتَلَ مُؤْمِنًا مُتَعَمِّدًا دُفِعَ إِلَى أَوْلِيَاءِ الْمَقْتُولِ فَإِنْ شَاءُوا قَتَلُوا وَإِنْ شَاءُوا أَخَذُوا الدِّيَةَ وَهِيَ ثَلاَثُونَ حِقَّةً وَثَلاَثُونَ جَذَعَةً وَأَرْبَعُونَ خَلِفَةً وَمَا صَالَحُوا عَلَيْهِ فَهُوَ لَهُمْ . وَذَلِكَ لِتَشْدِيدِ الْعَقْلِ . قَالَ أَبُو عِيسَى حَدِيثُ عَبْدِ اللَّهِ بْنِ عَمْرٍو حَدِيثٌ حَسَنٌ غَرِيبٌ .
Tirmizi
The Book on Blood Money • Hadith 1400