Nafi' narrates from Sayyiduna Ibn Umar (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) saw Sayyiduna Umar (may Allah be pleased with him) on a journey swearing by his father, so he (peace and blessings be upon him) said: "Allah forbids you from swearing by your fathers. Whoever wishes to swear, let him swear by Allah or remain silent."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19824