Musnad Abu Ya'la al-Mawsili 160:53

Daud ibn 'Amr al-Dabbi narrated to us, 'Isa ibn Yunus narrated to us, from al-Awza'i, from al-Zuhri, from Sa'id ibn al-Musayyib, who said: Abu Hurayrah narrated to me that 'Umar entered the mosque while the Abyssinians were playing. He rebuked them, but the Messenger of Allah (peace be upon him) said: "Leave them, for they are the sons of Arfida."