Musnad Ahmad 25:528

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, who said: Al-'Abbas ibn 'Abdullah ibn Ma'bad ibn 'Abbas narrated to me, from some of his family, from 'Abdullah ibn 'Abbas, that he used to say: "The Messenger of Allah, peace and blessings of Allah be upon him, used to recite in his two rak'ahs before the dawn prayer the Opening of the Book (Al-Fatihah) and the two verses from the end of Al-Baqarah in the first rak'ah. And in the other rak'ah, he would recite the Opening of the Book (Al-Fatihah) and the verse from Al-'Imran: 'Say, O People of the Scripture, come to a word that is equitable between us and you' [Al-'Imran: 64], until he finished the verse."