«إِنِّي مَا قَتَلْتُ ابْنَكَ سَهْوًا وَلَا عَمْدًا»
I did not kill your son, either inadvertently or intentionally.
Sahwan / ʿamdan contrast an unintended act with a deliberate one. Mā negates the past verb qataltu; both adverbial expressions specify the manner of the alleged action. The elder demands a comprehensive denial in a specially composed formula.