Musnad Ahmad 541:9

Rawh narrated to us, Ibn Jurayj narrated to us, Sa’id ibn Kathir informed me, that Ja’far ibn al-Muttalib informed him, that ‘Abdullah ibn ‘Amr ibn al-‘As entered upon ‘Amr ibn al-‘As. He invited him to lunch, and he said: "I am fasting." Then the second time [he invited him] likewise, then the third time. He said: "No, unless you heard it from the Messenger of Allah, may Allah bless him and grant him peace." He said: "I indeed heard it from the Messenger of Allah, may Allah bless him and grant him peace."