Musannaf Ibn Abi Shayba 3:5429

Abu Bakr narrated to us, he said: Waki' narrated to us, he said: Ibn Abi Khalid narrated to us, from Abu Salih, the freed slave of Umm Hani, from Umm Hani, she said: The Messenger of Allah (may Allah bless him and grant him peace) entered upon me in my house on the day of the conquest of Makkah. I placed water for him, so he performed ghusl. Then he prayed eight rak'ahs of the Duha prayer; he did not pray them before that day, nor after it.