Maliks Muwatta Book 56, Hadith Number 12.
Section : What is Feared from the Tongue.
Malik related to me from Zayd ibn Aslam from his father that Umar ibn al-Khattab came upon Abu Bakr as-Siddiq pulling his tongue. Umar said to him, “Stop, may Allah forgive you!” Abu Bakr replied, “This has brought me to dangerous places.”