Musnad Ahmad 27:1848

Ya'la narrated to us, Fudayl—meaning Ibn Ghazwan—narrated to us, from Abu Dihqana, from Ibn Umar, who said: There were people with the Prophet, may Allah bless him and grant him peace, and he called for Bilal regarding some dates he had. He brought dates that the Messenger of Allah, may Allah bless him and grant him peace, disapproved of. He said: "What are these dates?" He said: "The dates that were with us; we exchanged two sa's for one sa'." He said: "Return our dates to us."