Sayyiduna Uqbah bin Amir (may Allah be pleased with him) says: The Messenger of Allah (peace and blessings be upon him) commanded me to recite the Mu'awwidhat Surahs after every prayer.
Hadith Referenceالفتح الربانی / أبواب الأذ كار الواردة عقب الصلاة / 1881