Musnad Ahmad 31:31

Muhammad ibn Abi ‘Adi narrated to us, from Dawud, from Abu Nadrah, from Abu Sa’id, who said: We waited for the Messenger of Allah, peace and blessings of Allah be upon him, one night for the Isha prayer until about half of the night had passed. He said: So he came and led us in prayer, then he said: "Take your places, for the people have taken to their beds, and you will continue to be in a state of prayer as long as you are waiting for it. Were it not for the weakness of the weak, the illness of the sick, and the need of those who have needs, I would have delayed this prayer until half of the night."