Musnad Ahmad 20:11

Sufyan narrated to us, Ja'far bin Khalid narrated to us, from his father, from Abdullah bin Ja'far, who said: When the news of the death of Ja'far came when he was killed, the Prophet (peace and blessings of Allah be upon him) said: "Prepare food for the family of Ja'far, for there has come to them a matter that occupies them — or there has come to them that which occupies them."