Musnad Ahmad 27:285

Ibn Numayr narrated to us, Ubayd Allah narrated to us, from Nafi’, from Ibn Umar, that the Messenger of Allah (ﷺ) made a contract with the people of Khaybar for half of what came out of it of crops or dates. He used to give his wives every year one hundred wasqs: eighty wasqs of dates and twenty wasqs of barley. When Umar ibn al-Khattab stood up, he divided Khaybar, and he gave the wives of the Prophet (ﷺ) the choice: either he would allot land for them, or he would guarantee the wasqs for them every year. They differed; some of them chose to have land allotted to them, and some of them chose the wasqs. Hafsa and Aisha were among those who chose the wasqs.