"From the gravest of lies is someone who ascribes himself to other than his biological father, or claims to have seen something in a dream which he actually never saw, or ascribes something to the Messenger of Allah (may Allah's peace and blessings be upon him) which he did not say." [Al-Bukhari]

قَالَ رَسُولُ اللَّهِ ﷺ : " إِنَّ مِنْ أَعْظَمِ الْفِرَى أَنْ يَدَّعِيَ الرَّجُلُ إِلَى غَيْرِ أَبِيهِ أَوْ يُرِيَ عَيْنَهُ مَا لَمْ تَرَ أَوْ، يَقُولُ: عَلَى رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مَا لَمْ يَقُلْ ". صحيح البخاري