﴿ وَلَوْ نَشَآءُ لَأَرَيْنَٰكَهُمْ فَلَعَرَفْتَهُم بِسِيمَٰهُمْ ۚ وَلَتَعْرِفَنَّهُمْ فِى لَحْنِ ٱلْقَوْلِ ۚ وَٱللَّهُ يَعْلَمُ أَعْمَٰلَكُمْ ﴾

“Now had We so willed, We could have shown them clearly to thee, so that thou wouldst know them for sure as by a visible mark: but [even so,] thou wilt most certainly recognize them by the tone of their voice. And God knows all that you do, [O men;]”

Please check ayah 47:31 for complete tafsir.