Ya'la bin Mamlak says that I asked Umm Salama (may Allah be pleased with her) about the night prayer and recitation of the Prophet (peace be upon him), so she said: The Prophet (peace be upon him) used to sleep for as long as he prayed after performing the 'Isha prayer and the voluntary prayers, and he used to pray for as long as he slept, then the end of the Prophet's (peace be upon him) prayer would be at dawn.