﴿ إِنْ هُوَ إِلَّا رَجُلٌ ٱفْتَرَىٰ عَلَى ٱللَّهِ كَذِبًۭا وَمَا نَحْنُ لَهُۥ بِمُؤْمِنِينَ ﴾

“He is nothing but a man who attributes his own lying in­ventions to God, and we are not going to believe him!””

(He is only a man) they mean the Messenger is only a man (who hath invented a lie about Allah) in that which he says. (We are not going to put faith in him) we are not going to believe what he says.