Musnad Ahmad 31:170

Yazid narrated to us, Hammam ibn Yahya informed us, from Zayd ibn Aslam, from ‘Ata’ ibn Yasar, from Abu Sa’id al-Khudri, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not write anything from me except the Qur’an. Whoever has written anything from me other than the Qur’an, let him erase it."