Musnad Ahmad 830:22

Isma'il ibn Ibrahim narrated to us, al-Jariri narrated to us, 'Abd al-Rahman ibn Abi Bakrah narrated to us, from his father, who said: The major sins were mentioned in the presence of the Prophet, may Allah bless him and grant him peace, and he said: "Associating partners with Allah, and disobedience to parents." He had been reclining, then he sat up and said: "And false testimony, and false testimony," or "false speech." The Messenger of Allah, may Allah bless him and grant him peace, continued to repeat it until we said: "If only he would be silent." And he said on another occasion: Al-Jariri informed us, 'Abd al-Rahman ibn Abi Bakrah narrated to us, from his father, who said: We were sitting with the Prophet, may Allah bless him and grant him peace, and he said: "Shall I not inform you of the greatest of the major sins? Associating partners with Allah..." and he mentioned it.