Musannaf Ibn Abi Shayba 28:1050

Yazid narrated to us, he said: Hajjaj informed us, from Qatadah, from al-Hasan, from Samurah ibn Jundub, he said: The watchword of the Emigrants (Muhajirun) was "Abdullah," and the watchword of the Helpers (Ansar) was "Abdurrahman."