Musannaf Ibn Abi Shayba 23:184

Abu Usama narrated to us, from Ibn al-Mubarak, from Yunus, from al-Zuhri, from Hamza ibn Abdullah, from Ibn Umar, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I saw in a dream as if milk was flowing between my fingernail or my fingernails. Then I gave the remainder to Umar." He (the narrator) said: "How did you interpret it?" He said: "Knowledge."