Musannaf Ibn Abi Shayba 3:1686

Abu Bakr narrated to us, he said: Abu Mu'awiyah narrated to us, from Dawud ibn Abi Hind, from Abu Nadra, from Jabir, who said: The Prophet, may Allah bless him and grant him peace, went out one night while his companions were waiting for him for the final night prayer (Isha). He said: "The people have slept and slumbered, while you are waiting for the prayer. As for you, you are in a state of prayer as long as you are waiting for it. And were it not for the weakness of the weak and the old age of the old, I would have delayed this prayer until the middle of the night."