It is narrated from Wathilah bin Asqa’ (may Allah be pleased with him) that the Prophet (ﷺ) said: “The greatest slander is that someone attributes to me something which I did not say, or that someone claims to have seen in a dream what he did not see (i.e., narrates a false dream), and that someone claims someone other than his father as his father.”
Hadith Referenceمسند الإمام الشافعي / كتاب فضائل قريش وغيرهم وأبواب متفرقة / 1807