Mishkat al-Masabih 3313
She said:
One day God's Messenger visited me looking pleased and asked if I was not surprised to hear that Mujazziz al-Mudlijl 1 had entered, and seeing Usama and Zaid 2 with a rug over them covering their heads and letting their feet appear, said, “These feet are related.” 

(Bukhari and Muslim.)

1. Members of the tribe of Mudlij were said to have a reputation for being able to trace relationship from physical features.
2. Usama was Zaid's son.
وَعَنْهَا قَالَتْ: دَخَلَ عَلَى رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ ذَاتَ يَوْمٍ وَهُوَ مَسْرُورٌ فَقَالَ: 
" أَيْ عَائِشَةُ أَلَمْ تَرَيْ أَنَّ مُجَزِّزًا الْمُدْلِجِيَّ دَخَلَ فَلَمَّا رَأَى أُسَامَةَ وَزَيْدًا وَعَلَيْهِمَا قطيفةٌ قد غطيَّا رؤوسَهُما وَبَدَتْ أَقْدَامُهُمَا فَقَالَ: إِنَّ هَذِهِ الْأَقْدَامَ بَعْضُهَا من بعضٍ "