Musnad Ahmad 1012:109

I read to Ya'qub ibn Ibrahim, from his father, from Ibn Ishaq, who said: "Ubada ibn al-Samit ibn Qays ibn Asram ibn Fihr ibn Tha'labah ibn Ghanam ibn 'Awf ibn al-Khazraj was among the twelve who pledged allegiance to the Messenger of Allah, may Allah bless him and grant him peace, at the first [pledge of] al-'Aqabah."