The Prophet ﷺ said, "If somebody claims to be the son of any other than his real father knowingly, he but disbelieves in Allah, and if somebody claims to belong to some folk to whom he does not belong, let such a person take his place in the (Hell) Fire."  

أَنَّهُ سَمِعَ النَّبِيَّ ﷺ يَقُولُ لَيْسَ مِنْ رَجُلٍ ادَّعَى لِغَيْرِ أَبِيهِ وَهْوَ يَعْلَمُهُ إِلاَّ كَفَرَ وَمَنِ ادَّعَى قَوْمًا لَيْسَ لَهُ فِيهِمْ فَلْيَتَبَوَّأْ مَقْعَدَهُ مِنَ النَّارِ  

The Prophet ﷺ said, "Do not deny your fathers (i.e. claim to be the sons of persons other than your fathers), and whoever denies his father, is charged with disbelief."  

عَنِ النَّبِيِّ ﷺ قَالَ لاَ تَرْغَبُوا عَنْ آبَائِكُمْ فَمَنْ رَغِبَ عَنْ أَبِيهِ فَهُوَ كُفْرٌ  

I heard the Prophet ﷺ saying, "Whoever claims to be the son of a person other than his father, and he knows that person is not his father, then Paradise will be forbidden for him." I mentioned that to Abu Bakra, and he said, "My ears heard that and my heart memorized it from Messenger of Allah ﷺ.  

سَمِعْتُ النَّبِيَّ ﷺ يَقُولُ مَنِ ادَّعَى إِلَى غَيْرِ أَبِيهِ وَهْوَ يَعْلَمُ أَنَّهُ غَيْرُ أَبِيهِ فَالْجَنَّةُ عَلَيْهِ حَرَامٌ فَذَكَرْتُهُ لأَبِي بَكْرَةَ فَقَالَ وَأَنَا سَمِعَتْهُ أُذُنَاىَ وَوَعَاهُ قَلْبِي مِنْ رَسُولِ اللَّهِ ﷺ