Malik related to me from Yahya ibn Said from Said ibn al-Musayyab that a Syrian man called Ibn Khaybari found a man with his wife and killed him, or killed them both. Muawiya ibn Abi Sufyan found it difficult to make a decision and he wrote to Abu Musa al-Ashari to ask Ali ibn Abi Talib for him about that. So Abu Musa asked Ali ibn Abi Talib and AIi said to him, "Is this thing in my land? I adjure you, you must tell me." Abu Musa explained to him how Muawiya ibn Abi Sufyan had written him to ask Ali about it. Ali said, "I am Abu Hasan. If he does not bring four witnesses, then let him be completely handed over," (to the relatives of the murdered man).

وَحَدَّثَنِي مَالِكٌ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، أَنَّ رَجُلاً، مِنْ أَهْلِ الشَّامِ - يُقَالُ لَهُ ابْنُ خَيْبَرِيٍّ - وَجَدَ مَعَ امْرَأَتِهِ رَجُلاً فَقَتَلَهُ أَوْ قَتَلَهُمَا مَعًا فَأَشْكَلَ عَلَى مُعَاوِيَةَ بْنِ أَبِي سُفْيَانَ الْقَضَاءُ فِيهِ فَكَتَبَ إِلَى أَبِي مُوسَى الأَشْعَرِيِّ يَسْأَلُ لَهُ عَلِيَّ بْنَ أَبِي طَالِبٍ عَنْ ذَلِكَ فَسَأَلَ أَبُو مُوسَى عَنْ ذَلِكَ عَلِيَّ بْنَ أَبِي طَالِبٍ فَقَالَ لَهُ عَلِيٌّ إِنَّ هَذَا الشَّىْءَ مَا هُوَ بِأَرْضِي عَزَمْتُ عَلَيْكَ لَتُخْبِرَنِّي ‏.‏ فَقَالَ لَهُ أَبُو مُوسَى كَتَبَ إِلَىَّ مُعَاوِيَةُ بْنُ أَبِي سُفْيَانَ أَنْ أَسْأَلَكَ عَنْ ذَلِكَ ‏.‏ فَقَالَ عَلِيٌّ أَنَا أَبُو حَسَنٍ إِنْ لَمْ يَأْتِ بِأَرْبَعَةِ شُهَدَاءَ فَلْيُعْطَ بِرُمَّتِهِ ‏.‏
USC-MSA web (English) reference : Book 36, Hadith 18
Arabic reference : Book 36, Hadith 1422