Musannaf Ibn Abi Shayba 3:5437

Ghundar narrated to us, from Shu'bah, from al-Hakam, from a man, from Umm Salamah, that she used to pray the Duha prayer [consisting of] eight rak'ahs while she was sitting. It was said to her, "Indeed, 'Aishah prays four." She said, "Indeed, 'Aishah is a young woman."