Abu Qabil al-Ma'afiri (may Allah have mercy on him) says that Amr bin al-As (may Allah be pleased with him) came to Umar bin al-Khattab (may Allah be pleased with him), and he had dyed the hair of his head and beard black. Umar (may Allah be pleased with him) said: Who are you? He said: I am Amr bin al-As. Umar (may Allah be pleased with him) said: As I knew you, you were an old man, and today you are young! I adjure you to go out and wash off this black.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب القسم والنشوز / 14825