It is narrated from Abu al-Nadr Salim that a man came to Sayyiduna Ibn Umar (may Allah be pleased with them both) and greeted him with salam. He asked: "Who are you?" He said: "I am so-and-so, the one who brought you up." Ibn Umar (may Allah be pleased with them both) saw a black mark between his eyes and asked: "What is this mark between your eyes? I kept the company of the Messenger of Allah (peace and blessings be upon him), Abu Bakr, Umar and Uthman (may Allah be pleased with them); did you see anything like it there?"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3556