Musannaf Ibn Abi Shayba 36:513

Ibn Idris narrated to us, from Ibn ‘Ajlan, from Zayd ibn Aslam, from his father, who said: ‘Umar entered upon Abu Bakr while he was holding his tongue, pulling it. ‘Umar said to him, “Fear Allah, O Caliph of the Messenger of Allah!” He said, “This [tongue] is what brought me to the sources of destruction.”