Sayyiduna Ibn Umar (may Allah be pleased with them both) said: I was with the Messenger of Allah (peace and blessings be upon him). A man passed by the Prophet (peace and blessings be upon him), asking him for something. He (peace and blessings be upon him) said: "O Ibn Umar, do you know him?" I said: Yes. He (peace and blessings be upon him) asked: "What is his name?" I said: I do not know. He (peace and blessings be upon him) asked: "Where is his house?" I said: I do not know. He (peace and blessings be upon him) said: "This is not knowing him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20398