Musnad Ahmed: Hadith 2625

How old was the Messenger of Allah (ﷺ) on the day he died? He said: I did not think that a man of such standing among his people as you would be unaware of that. I said: I asked the people and they gave me different answers. I want to know what you say. He said: Do you know how to count? I said: Yes. He said: Bear in mind that he was sent as a Prophet when he was forty. Fifteen years in Makkah, with times of safety and times of fear, and ten years in Madinah after he migrated.