Musnad Ahmad 1117:2

Ibrahim ibn Khalid narrated to us, Rabah narrated to us, from Ma'mar, from al-Zuhri, from 'Abd al-Rahman ibn 'Abd Allah ibn Ka'b ibn Malik, from his mother, that Umm Mubashir entered upon the Messenger of Allah (may Allah bless him and grant him peace) during his illness in which he passed away. She said: "May my father and mother be sacrificed for you, O Messenger of Allah, what do you suspect regarding your condition? For I do not suspect anything except the food that was eaten with you at Khaybar." Her son had died before the Prophet (may Allah bless him and grant him peace). He said: "And I do not suspect anything other than it; this is the time my aorta is being severed."