Musnad Abu Ya'la al-Mawsili 3:267

Abu Abd al-Rahman al-Adhrami narrated to us, Ali ibn Yazid al-Suda'i narrated to us, from al-Harith ibn Nabhan, from Abu Ishaq, from al-Harith, from Ali, who said: The Messenger of Allah (may Allah bless him and grant him peace) forbade female singers and female mourners, and forbade buying them, selling them, and trading in them. And he said: "Their earnings are unlawful."