Musnad Abu Ya'la al-Mawsili 151:83

Sa'id ibn Ash'ath narrated to us, 'Abd al-Malik ibn al-Walid ibn Ma'dan informed me, 'Asim (meaning ibn Bahdalah) narrated to us, from Zirr ibn Hubaysh, from 'Abdullah ibn Mas'ud, who said: I cannot count how many times I heard the Messenger of Allah (may Allah bless him and grant him peace) reciting in the two rak'ahs before the dawn prayer and in the two rak'ahs after the Maghrib prayer: "Say, 'O disbelievers'" (Surah Al-Kafirun) and "Say, 'He is Allah, [who is] One'" (Surah Al-Ikhlas).