The Prophet ﷺ said: Do not swear by your fathers, or by your mothers, or by rivals to Allah; and swear by Allah only, and swear by Allah only when you are speaking the truth.  

قَالَ رَسُولُ اللَّهِ ﷺ لاَ تَحْلِفُوا بِآبَائِكُمْ وَلاَ بِأُمَّهَاتِكُمْ وَلاَ بِالأَنْدَادِ وَلاَ تَحْلِفُوا إِلاَّ بِاللَّهِ وَلاَ تَحْلِفُوا بِاللَّهِ إِلاَّ وَأَنْتُمْ صَادِقُونَ  

The Messenger of Allah ﷺ found 'Umar al-Khattab in a caravan while he was swearing by his father. So he said: Allah forbids you to swear by forefathers. If anyone swears, he must swear by Allah or keep silence.  

أَنَّ رَسُولَ اللَّهِ ﷺ أَدْرَكَهُ وَهُوَ فِي رَكْبٍ وَهُوَ يَحْلِفُ بِأَبِيهِ فَقَالَ إِنَّ اللَّهَ يَنْهَاكُمْ أَنْ تَحْلِفُوا بِآبَائِكُمْ فَمَنْ كَانَ حَالِفًا فَلْيَحْلِفْ بِاللَّهِ أَوْ لِيَسْكُتْ  

" 'Umar said: I swear by Allah, I never swore by it personally or reporting it from others."  

سَمِعَنِي رَسُولُ اللَّهِ ﷺ نَحْوَ مَعْنَاهُ إِلَى بِآبَائِكُمْ زَادَ قَالَ عُمَرُ فَوَاللَّهِ مَا حَلَفْتُ بِهَذَا ذَاكِرًا وَلاَ آثِرًا  

Ibn Umar heard a man swearing: No, I swear by the Ka'bah. Ibn Umar said to him: I heard the Messenger of Allah ﷺ say: He who swears by anyone but Allah is polytheist.  

سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ مَنْ حَلَفَ بِغَيْرِ اللَّهِ فَقَدْ أَشْرَكَ  

He became successful, by his father, if he speaks the truth, he will enter paradise, by his father, if he speaks truth.  

قَالَ النَّبِيُّ ﷺ أَفْلَحَ وَأَبِيهِ إِنْ صَدَقَ دَخَلَ الْجَنَّةَ وَأَبِيهِ إِنْ صَدَقَ