Maliks Muwatta Book 054, Hadith Number 044.

Section : The Slave and his Reward.

Malik related to me that he heard that Umar ibn al-Khattab saw a female slave belonging to Abdullah ibn Umar ibn al-Khattab. She was dressed up in silks. He went to his daughter Hafsa and said, "Didn't I see your brother's slave-girl dressed up in silks walking among the people and causing trouble?" Umar disapproved of that.