Umar entered while the Abyssinians were playing in the mosque, and he scolded them. The Messenger of Allah ﷺ said, "Let them be, Umar, for they are the sons of Arfidah."
أخبرنا إسحق بن موسى قال حدثنا الوليد بن مسلم قال حدثنا الأوزاعي قال حدثني الزهري عن سعيد بن المسيب
دخل عمر والحبشة يلعبون في المسجد فزجرهم عمر رضي الله عنه فقال رسول الله ﷺ دعهم يا عمر فإنما هم بنو أرفدة
Bukhari narrated it in the Book of Jihad and Expeditions, chapter on playing with spears and the like, hadith no. 2901, and Muslim in the Book of the Two Eids, chapter on the permission for play, hadith no. 22/893, from the hadith of Zuhri, through him. It is also in Al-Kubra, hadith no. 1799.