"The Messenger of Allah said: 'Whoever swears, let him not swear by anything other than Allah.'" The Quraish used to swear by their forefathers, and so he said: "Do not swear by your forefathers."
قَالَ رَسُولُ اللَّهِ ﷺ مَنْ كَانَ حَالِفًا فَلاَ يَحْلِفْ إِلاَّ بِاللَّهِ وَكَانَتْ قُرَيْشٌ تَحْلِفُ بِآبَائِهَا فَقَالَ لاَ تَحْلِفُوا بِآبَائِكُمْ