Sahih al-Bukhari 6646
Sahih al-Bukhari · Book 83: Oaths and Vows · "Do not swear by your fathers"
Narrated Ibn `Umar:
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ ، عَنْ مَالِكٍ ، عَنْ نَافِعٍ ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم أَدْرَكَ عُمَرَ بْنَ الْخَطَّابِ وَهْوَ يَسِيرُ فِي رَكْبٍ يَحْلِفُ بِأَبِيهِ فَقَالَ " أَلاَ إِنَّ اللَّهَ يَنْهَاكُمْ أَنْ تَحْلِفُوا بِآبَائِكُمْ، مَنْ كَانَ حَالِفًا فَلْيَحْلِفْ بِاللَّهِ، أَوْ لِيَصْمُتْ " .
Allah's Messenger (ﷺ) met `Umar bin Al-Khattab while the latter was going with a group of camel-riders, and he was swearing by his father. The Prophet (ﷺ) said, "Lo! Allah forbids you to swear by your fathers, so whoever has to take an oath, he should swear by Allah or keep quiet."