"My maternal aunt took me to the Prophet ﷺ, and said: 'O Messenger of Allah! Indeed my nephew is in pain.' So he wiped over my head and supplicated for blessings for me. And he performed Wudu and I drank from the water of his Wudu. Then I stood behind his back, and I looked at the seal between his two shoulder blades, and it resembled the egg of a partridge.  

سَمِعْتُ السَّائِبَ بْنَ يَزِيدَ يَقُولُ ذَهَبَتْ بِي خَالَتِي إِلَى النَّبِيِّ ﷺ فَقَالَتْ يَا رَسُولَ اللَّهِ إِنَّ ابْنَ أُخْتِي وَجِعٌ فَمَسَحَ بِرَأْسِي وَدَعَا لِي بِالْبَرَكَةِ وَتَوَضَّأَ فَشَرِبْتُ مِنْ وَضُوئِهِ فَقُمْتُ خَلْفَ ظَهْرِهِ فَنَظَرْتُ إِلَى الْخَاتَمِ بَيْنَ كَتِفَيْهِ فَإِذَا هُوَ مِثْلُ زِرِّ الْحَجَلَةِ  

"The seal of the Messenger of Allah ﷺ" - meaning the one which was between his two shoulder blades - "was fleshy and red, resembling the egg of a pigeon."  

كَانَ خَاتَمُ رَسُولِ اللَّهِ ﷺ يَعْنِي الَّذِي بَيْنَ كَتِفَيْهِ غُدَّةً حَمْرَاءَ مِثْلَ بَيْضَةِ الْحَمَامَةِ