Sunan an-Nasa'i 1628

Ya'la bin Mamlak said that he asked Umm Salamah about the prayer of the Messenger of Allah (ﷺ) and she said:"He used to pray 'Isha, then he would recite tasbih, then after that he would pray whatever Allah (SWT) willed (he should pray) of night prayer. Then he would go and sleep for as long as he had prayed. Then he would get up from sleep and pray for as long as he had slept, and this last prayer of his would continue until dawn