Musnad Abu Ya'la al-Mawsili 1:5

Musa ibn Muhammad ibn Hayyan narrated to us, Abd al-Samad ibn Abd al-Warith informed us, Abd al-Aziz al-Darawardi informed us, from Zayd ibn Aslam, from his father, that Umar looked upon Abu Bakr while he was pulling his tongue. He said, "What are you doing, O Caliph of the Messenger of Allah?" He replied, "This is what has brought me to the sources [of destruction]. The Messenger of Allah, may Allah bless him and grant him peace, said: 'There is no part of the body but that it complains about the sharpness of the tongue.'"