Allah, the Great and Majestic, forbids you to swear by your fathers. Umar said: By Allah. I have never sworn (by my father) since I heard Messenger of Allah ﷺ forbidding it mentioning them" on my behalf" nor on behalf of someone else.
قَالَ رَسُولُ اللَّهِ ﷺ إِنَّ اللَّهَ ﷻ يَنْهَاكُمْ أَنْ تَحْلِفُوا بِآبَائِكُمْ قَالَ عُمَرُ فَوَاللَّهِ مَا حَلَفْتُ بِهَا مُنْذُ سَمِعْتُ رَسُولَ اللَّهِ ﷺ نَهَى عَنْهَا ذَاكِرًا وَلاَ آثِرًا