Musnad Ahmad 922:9

Abdullah narrated to us, Ibrahim ibn Isma'il ibn Yahya ibn Salamah ibn Kuhayl narrated to me, from my father, from his father, from Salamah, from Sa'id ibn 'Abd al-Rahman ibn Abza, from his father, from Ubayy ibn Ka'b, who said: The Messenger of Allah (peace and blessings of Allah be upon him) used to teach us when we reached the morning: "We have reached the morning upon the natural disposition (fitrah) of Islam, the word of sincerity, the Sunnah of our Prophet Muhammad (peace and blessings of Allah be upon him), and the religion of our father Ibrahim, inclining toward truth, a Muslim, and he was not of the polytheists." And when we reached the evening, we would say the same.