Muwatta Malik, Book 43, Hadith 1558 (In-Book) ⓘ

Yahya related to me from Malik from Yahya ibn Said that Marwan ibn al-Hakam wrote to Muawiya ibn Abi Sufyan that a madman was brought to him who had killed a man. Muawiya wrote to him, "Tie him up and do not inflict any retaliation on him. There is no retaliation against a madman." Malik said about an adult and a child when they murder a man together, "The adult is killed and the child pays half the full blood-money." Malik said, "It is like that with a freeman and a slave when they murder a slave. The slave is killed and the freeman pays half of his value."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، أَنَّ مَرْوَانَ بْنَ الْحَكَمِ، كَتَبَ إِلَى مُعَاوِيَةَ بْنِ أَبِي سُفْيَانَ أَنَّهُ أُتِيَ بِمَجْنُونٍ قَتَلَ رَجُلاً ‏.‏ فَكَتَبَ إِلَيْهِ مُعَاوِيَةُ أَنِ اعْقِلْهُ وَلاَ تُقِدْ مِنْهُ فَإِنَّهُ لَيْسَ عَلَى مَجْنُونٍ قَوَدٌ ‏.‏ قَالَ مَالِكٌ فِي الْكَبِيرِ وَالصَّغِيرِ إِذَا قَتَلاَ رَجُلاً جَمِيعًا عَمْدًا أَنَّ عَلَى الْكَبِيرِ أَنْ يُقْتَلَ وَعَلَى الصَّغِيرِ نِصْفُ الدِّيَةِ ‏.‏ قَالَ مَالِكٌ وَكَذَلِكَ الْحُرُّ وَالْعَبْدُ يَقْتُلاَنِ الْعَبْدَ فَيُقْتَلُ الْعَبْدُ وَيَكُونُ عَلَى الْحُرِّ نِصْفُ قِيمَتِهِ ‏.‏