Musnad Abu Ya'la al-Mawsili 128:28

Abu al-Walid al-Qurashi narrated to us, al-Walid narrated to us, and he said: Salim informed me that he heard Muhammad ibn ‘Amr ibn ‘Uthman narrating from Anas ibn Malik, that al-Juhani said: "O Messenger of Allah, we are where you know, and we are not able to be present for the [entire] month, so inform us of the Night of Decree." He said: "Be present for the last seven [nights] of the month." He said: "I am not able to do that." He said: "Seek it on the seventh night remaining, and it is this night." He said: "I said: 'O Messenger of Allah, this is the night of the twenty-third, and it is for eight remaining.'" He said: "It is like this; this month decreases, and it is seven remaining."