Musannaf Ibn Abi Shayba 33:265

Yazid ibn Harun narrated to us, from Muhammad ibn Mutarrif, from Zayd ibn Aslam, from his father, who said: I used to bring Umar a *sa'* of dates, and he would say, "O Aslam, scrape off the skin from it for me," and he would remove the bad ones, then he would eat it.