Musnad Ahmad 1153:265

Yahya narrated to us, from Ubaydullah, who said: I heard al-Qasim narrating from Aisha, who said: "How evil is what you have equated us with: the dog and the donkey. I have seen the Messenger of Allah (peace and blessings of Allah be upon him) praying while I was lying across between his hands. When he wanted to prostrate, he would pinch—meaning my legs—so I would draw them in toward me, and then he would prostrate."