Sahih Al Bukhari (190)

حَدَّثَنَا عَبْدُالرَّحْمَنِ بْنُ يُونُسَ، قَالَ: حَدَّثَنَا حَاتِمُ بْنُ إِسْمَاعِيلَ، عَنِ الجَعْدِ، قَالَ: سَمِعْتُ السَّائِبَ بْنَ يَزِيدَ، يَقُولُ: ذَهَبَتْ بِي خَالَتِي إِلَى النَّبِيِّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ فَقَالَتْ: يَا رَسُولَ اللَّهِ، إِنَّ ابْنَ أُخْتِي وَجِعٌ "فَمَسَحَ رَأْسِي وَدَعَا لِي بِالْبَرَكَةِ، ثُمَّ تَوَضَّأَ، فَشَرِبْتُ مِنْ وَضُوئِهِ، ثُمَّ قُمْتُ خَلْفَ ظَهْرِهِ، فَنَظَرْتُ إِلَى خَاتَمِ النُّبُوَّةِ بَيْنَ كَتِفَيْهِ، مِثْلَ زِرِّ الحَجَلَةِ"

As-Sa'ib ibn Yazid (may Allah be pleased with him) narrated: My aunt took me to the Prophet (peace be upon him) and said: "O Allah’s Messenger (peace be upon him)! This son of my sister has got a disease in his legs." So, he passed his hands on my head and prayed for Allah’s blessings for me; then he performed ablution and I drank from the remaining water. I stood behind him and saw the seal of Prophethood between his shoulders, and it was like the "Zir-al-Hijla" (means the button of a small tent, but some said: 'egg of a partridge.' etc.)