﴿ وَإِذَا رَأَوْكَ إِن يَتَّخِذُونَكَ إِلَّا هُزُوًا أَهَٰذَا ٱلَّذِى بَعَثَ ٱللَّهُ رَسُولًا ﴾

“Hence, whenever they consider thee, [O Muhammad,] they but make thee a target of their mockery, [saying:] “Is this the one whom God has sent as an apostle?”

Please check ayah 25:44 for complete tafsir.