(a) Sayyidah Aishah (may Allah be pleased with her), mentioning the night prayer, said: I said: O Messenger of Allah, do you sleep before praying witr? He (peace and blessings be upon him) said: "O Aishah, my eyes sleep but my heart does not sleep."
(b) Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him) that his eyes would sleep but his heart would not sleep, and likewise the eyes of all the prophets sleep but their hearts do not sleep.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 602