Musannaf Ibn Abi Shayba 3:5407

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: An-Nahhas ibn Qahm Abu al-Khattab narrated to us, from Shaddad Abu ‘Ammar ash-Shami, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever maintains the Duha prayer, his sins will be forgiven, even if they were like the foam of the sea."