Musannaf Ibn Abi Shayba 1:1401

Hushaym narrated to us, from Mughirah, from Ibrahim, that the Prophet, peace and blessings of Allah be upon him, slept in the mosque until he breathed heavily (snored), then he stood and prayed and did not perform ablution. The Prophet, peace and blessings of Allah be upon him, his eyes would sleep, but his heart would not sleep.