Musnad Ahmad

Sa’d bin Ubaidah (may Allah have mercy on him) says that I and Muhammad Kindi were sitting with Sayyiduna Ibn Umar (may Allah be pleased with them both). After a little while, I got up from there and went to sit with Sa’eed bin Musayyib (may Allah have mercy on him). Meanwhile, my companion came; the color of his face had changed and it was pale yellow. As soon as he arrived, he said, “Come with me.” I said, “I was just sitting with you.” Sa’eed bin Musayyib (may Allah have mercy on him) said, “Go with your companion.” So I stood up. He said to me, “Did you hear what Sayyiduna Ibn Umar (may Allah be pleased with them both) said?” I asked, “What did he say?” He said that a man came to him and said, “O Abu Abdur Rahman! If I swear by the Ka’bah, will there be any sin upon me?” He replied, “What need do you have to swear by the Ka’bah? If you must swear by the Ka’bah, then swear by the Lord of the Ka’bah, because Sayyiduna Umar (may Allah be pleased with him) used to swear by saying «كلا وابي». One day, even in the presence of the Prophet (peace and blessings be upon him), he swore this oath, so the Prophet (peace and blessings be upon him) said: ‘Do not swear by your father or by anything other than Allah, for whoever swears by other than Allah commits shirk (associating partners with Allah).’”