the Messenger of Allah ﷺ heard him swearing by his father. The Messenger of Allah ﷺ said: 'Allah forbids you from making oaths by your forefathers." 'Umar said: I never took an oath by them (i.e., my forefathers) myself nor narrating such words from anyone else.”
أَنَّ رَسُولَ اللَّهِ ﷺ سَمِعَهُ يَحْلِفُ بِأَبِيهِ فَقَالَ رَسُولُ اللَّهِ ﷺ إِنَّ اللَّهَ يَنْهَاكُمْ أَنْ تَحْلِفُوا بِآبَائِكُمْ قَالَ عُمَرُ فَمَا حَلَفْتُ بِهَا ذَاكِرًا وَلاَ آثِرًا