Musnad Ahmad 32:229

Asbat ibn Muhammad narrated to us, al-Taymi narrated to us, from Qatadah, from Anas, who said: The general [final] instruction of the Messenger of Allah, may Allah bless him and grant him peace, when death approached him, was: "The prayer, and what your right hands possess. The prayer, and what your right hands possess." Until the Messenger of Allah, may Allah bless him and grant him peace, began to gurgle with it in his chest, and his tongue could barely utter it.