Sahih Muslim Book 4, Hadith Number 1040.

Chapter : The excellence of the prayer and the way it is begun and the excellence of Ruku’ and moderation in it and prostration and moderation in it, etc.

‘Aisha reported: I was sleeping in front of the Messenger of Allah (may peace be upon him) with my legs between him and the Qibla. When he prostrated himself he pinched me and I drew up my legs, and when he stood up, I stretched them out. She said: At that time there were no lamps in the houses.