Musnad Abu Ya'la al-Mawsili 154:203

And from Abdullah, he said: The Messenger of Allah (peace and blessings of Allah be upon him) heard Umar while he was swearing by his father, and he was in a caravan traveling with them. So he called out to them, and the Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, Allah forbids you from swearing by your fathers. So whoever is to swear, let him swear by Allah or remain silent."