Musnad Abu Ya'la al-Mawsili 166:15

Mujahid ibn Musa narrated to us, Mu'awiyah ibn 'Amr narrated to us, Abu Ishaq al-Fazari narrated to us, from Sufyan ibn 'Uyaynah, from Ja'far ibn Khalid, from his father, from 'Abdullah ibn Ja'far, who said: When the death of Ja'far was announced, the Messenger of Allah (may Allah bless him and grant him peace) said: "Prepare food for the family of Ja'far, for there has come to them a matter that occupies them, or they are occupied by it."