Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrates from Umm Hani bint Abi Talib (may Allah be pleased with her) that "the Messenger of Allah (peace and blessings be upon him) one day prayed the voluntary Duha prayer of eight rak'ahs, saying the salam after every two rak'ahs."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21355