Musnad Ahmad 1153:2215

Yunus narrated to us, he said: Layth narrated to us, from Yazid—meaning Ibn al-Had—from Abd al-Rahman ibn al-Qasim, from al-Qasim ibn Muhammad, from Aisha, she said: "The Messenger of Allah, may Allah bless him and grant him peace, would pray while I was lying across in front of him like the lying of a funeral bier. When he intended to perform the witr, he would touch me with his foot, so I would know that he was performing the witr, and I would move back a little from in front of him."