Musnad Ahmad 98
It was narrated that Mujahid said:
A man struck a son of his with a sword and killed him. The matter was referred to 'Umar and he said. Were it not that I heard the Messenger of Allah ﷺ say, “No father should be executed in retaliation for killing his son.` I would have executed you before you left.
حَدَّثَنَا أَسْوَدُ بْنُ عَامِرٍ، قَالَ أَخْبَرَنَا جَعْفَرٌ يَعْنِي الْأَحْمَرَ، عَنْ مُطَرِّفٍ، عَنِ الْحَكَمِ، عَنْ مُجَاهِدٍ، قَالَ حَذَفَ رَجُلٌ ابْنًا لَهُ بِسَيْفٍ فَقَتَلَهُ فَرُفِعَ إِلَى عُمَرَ فَقَالَ لَوْلَا أَنِّي سَمِعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَقُولُ لَا يُقَادُ الْوَالِدُ مِنْ وَلَدِهِ لَقَتَلْتُكَ قَبْلَ أَنْ تَبْرَحَ‏.‏