It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that when the Noble Prophet (peace and blessings be upon him) heard Sayyiduna Umar (may Allah be pleased with him) saying, "By my father," the Prophet (peace and blessings be upon him) said: "Indeed, Allah Almighty forbids you from swearing by your forefathers. When anyone swears an oath, let him swear by Allah Almighty, or remain silent." Sayyiduna Umar (may Allah be pleased with him) said: "After that, I never intentionally swore such an oath, nor even while quoting someone else."