Musnad Abu Ya'la al-Mawsili 154:154

Abu Khaythama narrated to us, Muhammad ibn Khazim narrated to us, Suhayl narrated to us, from his father, from Ibn Umar, who said: We used to count, while the Messenger of Allah (peace and blessings of Allah be upon him) was alive and his companions were numerous: Abu Bakr, and Umar, and Uthman, then we would remain silent.