Musnad Ahmad 937:158

'Abd al-Razzaq narrated to us, Sufyan informed us, from Dawud ibn Abi Hind, from al-Walid ibn 'Abd al-Rahman al-Jurashi, from Jubayr ibn Nufayr al-Hadrami, from Abu Dharr, who said: We fasted Ramadan with the Messenger of Allah (may Allah bless him and grant him peace), and he did not stand [in prayer] with us for any part of the month until seven [nights] remained. Then he stood with us until about a third of the night had passed. Then he did not stand with us on the fourth night, but he stood with us on the night that followed it until about half of the night had passed. We said: "O Messenger of Allah, if only you had granted us extra prayer for the remainder of this night of ours." He said: "Indeed, when a man stands with the Imam until he departs, it is recorded for him as the remainder of his night." Then he did not stand with us on the sixth [night], but he stood with us on the seventh. He sent for his family and the people gathered, and he stood with us until we feared that we would miss the *falah*. I said: "And what is the *falah*?" He said: "The *suhur* (pre-dawn meal)."