Musnad Ahmad 25:494

Ubaydah narrated to us, Qabus narrated to me, from Abu Zabyan, from Ibn Abbas: That the Prophet of Allah, peace and blessings of Allah be upon him, came toward them quickly. He said: Until he alarmed us with his speed. When he reached us, he said: "I came quickly to inform you about the Night of Decree, but I was made to forget it between me and you. However, seek it in the last ten nights of Ramadan."