Musnad Ahmad 1156:224

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Abu 'Awn, from 'Abdullah ibn Shaddad, he said: Marwan said: "How can we ask anyone while the wives of the Prophet, may Allah bless him and grant him peace, are among us?" He said: So he sent to Umm Salamah, and she informed him "that the Messenger of Allah, may Allah bless him and grant him peace, went out for the prayer, and a shoulder [of meat] was pulled out for him from a pot, so he ate it, then he went out and prayed."