'Abdullah bin Mas'ud said:"It was said: 'O Messenger of Allah, how will you recognize those whom you have not seen of your Ummah?' He said: 'From the blazes of their foreheads and feet, like horses with black and white traces (which make them distinct from others) which are the traces of ablution.'" (Hasan) Another chain with similar wording.
حَدَّثَنَا مُحَمَّدُ بْنُ يَحْيَى النَّيْسَابُورِيُّ، حَدَّثَنَا أَبُو الْوَلِيدِ، هِشَامُ بْنُ عَبْدِ الْمَلِكِ حَدَّثَنَا حَمَّادٌ، عَنْ عَاصِمٍ، عَنْ زِرِّ بْنِ حُبَيْشٍ، أَنَّ عَبْدَ اللَّهِ بْنَ مَسْعُودٍ، قَالَ قِيلَ يَا رَسُولَ اللَّهِ كَيْفَ تَعْرِفُ مَنْ لَمْ تَرَ مِنْ أُمَّتِكَ قَالَ " غُرٌّ مُحَجَّلُونَ بُلْقٌ مِنْ آثَارِ الطُّهُورِ " . قَالَ أَبُو الْحَسَنِ الْقَطَّانُ حَدَّثَنَا أَبُو حَاتِمٍ، حَدَّثَنَا أَبُو الْوَلِيدِ، فَذَكَرَ مِثْلَهُ .
IbnMaja
The Book of Purification and its Sunnah • Hadith 284