ما كفارة شتم المرأة وأمّها بألفاظ قاسية في لحظة غضب، مع العلم أن الشاتم ملتزم ولا يشتم عادة؟

You must repent to Allah Almighty for the insults you uttered. No expiation is required of you other than repentance, because you do not know the woman who was insulted. Repentance involves abandoning the sin, regretting having committed it, and resolving never to return to it. We advise you to control yourself when angry, for anger is the root of all evil.