Musnad Ahmad 1153:2261

Abu Ahmad narrated to us, Abdullah—meaning Ibn Abd al-Rahman ibn Ya'la al-Thaqafi—narrated to us, from Abd al-Rahman ibn al-Qasim, from his father, from Aisha, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) would not sleep before the Isha prayer, nor would he stay up late after it."