Yahya bin Saeed narrated that Abdullah bin Umar (may Allah be pleased with them) was asked about an issue, but he did not give any answer. Then it was said to him: "We find it very (strange) that you are the son of two rightly guided Imams (i.e., Umar and Ibn Umar, may Allah be pleased with them), and you are asked about an issue while you do not have knowledge about it?" So he replied: "An even stranger thing in the sight of Allah, and for the one who recognizes Allah, and for the one who has understanding from Allah, is that I should say something about which I have no knowledge, or that I should narrate something from an unreliable (narrator)."
Hadith Referenceمسند الإمام الشافعي / كتاب فضائل قريش وغيرهم وأبواب متفرقة / 1813