Musnad Ahmad 27:1185

Abu Abd al-Rahman Abdullah ibn Yazid narrated to us, Sa'id—meaning Ibn Abi Ayyub—narrated to us, Abu Hani' narrated to us, from Abbas al-Hajari, from Abdullah ibn Umar ibn al-Khattab, that a man came to the Messenger of Allah, may Allah bless him and grant him peace, and said: "O Messenger of Allah, I have a servant who does wrong and acts unjustly; should I beat him?" He said: "Pardon him seventy times every day."