Musnad Ahmad 28:542

Muhammad ibn Yazid al-Wasiti narrated to us, Muhammad ibn Ishaq informed us, from ‘Amr ibn Shu‘ayb, from his father, from his grandfather ‘Abdullah ibn ‘Amr ibn al-‘As, who said: I said: "O Messenger of Allah, I hear things from you, should I write them down?" He said: "Yes." I said: "In anger and in pleasure?" He said: "Yes, for I do not say in them anything but the truth."