Lying about the Prophet (peace be upon him) is among the gravest sins. He said, "Whoever deliberately lies about me, let him take his seat in the Fire" — a narration so widely transmitted that the scholars graded it mutawatir, reported from more than sixty Companions and recorded by both al-Bukhari and Muslim. It was precisely to guard against such forgery that the early scholars built the science of isnad, so a fabricated (mawdu') report may never be presented as his speech. Even knowingly passing on a fabrication as if it were his falls under this warning.
Evidence — the daleel
Sahih al-Bukhari 110 (Kitab al-'Ilm) ṢaḥīḥSahih Muslim, Introduction (Muqaddimah)
On deen2u
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.