The Messenger of Allah ﷺ heard me swearing an oath by my father and said: “Allah forbids you to swear by your fathers.” ‘Umar said: By Allah, I never swore by my father after that, whether saying it myself or narrating what someone else had said. (Using translation from Aḥmad 241)
سَمِعَ النَّبِيَّ ﷺ عُمَرَ وَهُوَ يَقُولُ وَأَبِي وَأَبِي فَقَالَ «إِنَّ اللهَ يَنْهَاكُمْ أَنْ تَحْلِفُوا بِآبَائِكُمْ» قَالَ عُمَرُ فَوَاللهِ مَا حَلَفْتُ بِهَا بَعْدُ ذَاكِرًا وَلَا آثِرًا