Musnad Ahmad 1156:212

Rawh narrated to us, he said: Sa’id ibn Abi ‘Arubah narrated to us, from Qatadah, he said: Safinah, the freed slave of Umm Salamah, narrated from Umm Salamah, the wife of the Prophet, may Allah bless him and grant him peace, that the general [final] instruction of the Prophet of Allah, may Allah bless him and grant him peace, at the time of his death was: "The prayer, the prayer, and what your right hands possess." Until the Prophet of Allah, may Allah bless him and grant him peace, began to mumble it in his chest, and his tongue could not articulate it clearly.