Musnad Abu Ya'la al-Mawsili 2:58

Abu Khaythama narrated to us, Sufyan ibn 'Uyayna narrated to us, from Yahya ibn Sa'id, who heard it from 'Ubayd ibn Hunayn, from Ibn 'Abbas, who said: I wanted to ask 'Umar for nearly a year about the two women who supported one another against the Messenger of Allah (may Allah bless him and grant him peace), but I did not dare to ask him. We were at Marr al-Zahran, and he went to perform ablution. He said, "Bring me a vessel of water." I brought it to him, and I said, "O Commander of the Faithful, who were the two women?" I had not finished my speech before he said, "Aisha and Hafsa."