Indeed, Allah Almighty forbids you to swear by your forefathers
عَنْ عُمَرَ بْنِ الْخَطَّابِ رضي الله عنه قَالَ: قَالَ رَسُولُ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ: «إِنَّ اللهَ عَزَّ وَجَلَّ يَنْهَاكُمْ أَنْ تَحْلِفُوا بِآبَائِكُمْ»، قَالَ عُمَرُ: فَوَاللهِ مَا حَلَفْتُ بِهَا مُنْذُ سَمِعْتُ رَسُولَ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ نَهَى عَنْهَا ذَاكِرًا وَلَا آثِرًا.
Explanation
The Prophet (may Allah's peace and blessings be upon him) informed us that Allah Almighty forbids swearing by the forefathers. So, whoever wants to swear should swear by Allah only and none but Him. ‘Umar ibn al-Khattāb, then, mentioned that ever since he heard the Prophet (may Allah's peace and blessings be upon him) prohibit it, he never swore by other than Allah neither intentionally nor by reporting such an oath on behalf of others.
Source
Join 50,000+ Muslims
Download for free and never miss a prayer again