Narrated As-Sa'ib bin Yazid: My aunt took me to Allah's Messenger (ﷺ) and said, "O Allah's Messenger! My sister's son is sick." So he passed his hand over my head and invoked for Allah's blessing upon me and then performed the ablution. I drank from the water of his ablution and I stood behind him and looked at his Khatam (the seal of Prophethood) between his shoulders (and its size was) like the button of a tent.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا حَاتِمٌ، عَنِ الْجَعْدِ بْنِ عَبْدِ الرَّحْمَنِ، قَالَ سَمِعْتُ السَّائِبَ بْنَ يَزِيدَ، يَقُولُ ذَهَبَتْ بِي خَالَتِي إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم فَقَالَتْ يَا رَسُولَ اللَّهِ إِنَّ ابْنَ أُخْتِي وَجِعٌ. فَمَسَحَ رَأْسِي، وَدَعَا لِي بِالْبَرَكَةِ، ثُمَّ تَوَضَّأَ فَشَرِبْتُ مِنْ وَضُوئِهِ، ثُمَّ قُمْتُ خَلْفَ ظَهْرِهِ، فَنَظَرْتُ إِلَى خَاتَمِهِ بَيْنَ كَتِفَيْهِ مِثْلَ زِرِّ الْحَجَلَةِ.
sunnah.com