Sayyiduna Abdullah bin Umar (may Allah be pleased with him) says that the Prophet (peace and blessings be upon him) saw Sayyiduna Umar (may Allah be pleased with him) in a caravan, swearing by his father. The Prophet (peace and blessings be upon him) said: "Allah has forbidden you from swearing by your father. Whoever wishes to swear, let him swear by Allah or remain silent."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19823