Musnad Ahmad 27:1084

Muhammad narrated to us, Shu'bah narrated to us, from Jabalah ibn Suhaym, who said: Ibn al-Zubayr used to provide us with dates. He said: The people had been afflicted with hardship in those days, so we were eating. Ibn Umar would pass by us while we were eating and say: "Do not practice *iqran* (pairing dates), for the Messenger of Allah (peace be upon him) forbade *iqran*, unless a man asks his brother for permission." Shu'bah said: "I do not see the part about asking for permission as anything other than a statement from the words of Ibn Umar."