Musnad Ahmad 1153:296

Ibn Numayr narrated to us, Malik—meaning Ibn Mughul—narrated to us, from Muqatil ibn Bashir, from Shurayh ibn Hani, who said: I asked Aisha about the prayer of the Messenger of Allah, peace and blessings of Allah be upon him. She said: "There was no prayer that he was more inclined to delay, if he was engaged in a conversation, than the final night prayer (Isha). He never prayed it—meaning, he never entered upon me—without praying four or six [rak'ahs] after it. And I never saw him protect himself from the ground with anything at all, except that I remember on a rainy day we placed a garment (bata) beneath him, and it is as if I am looking at a hole in it from which water was springing."