Sahih al-Bukhari

Narrated As Saib bin Yazid
My aunt took me to the Prophet and said, "O Allah’s Apostle! 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.) (Volume 1, Book 4, Number 189)

Narrated As Saib
My aunt took me to Allah's Apostle and said, "O Allah's Apostle! My nephew is ill." The Prophet touched my head with his hand and invoked Allah to bless me. He then performed ablution and I drank of the remaining water of his ablution and then stood behind his back and saw "Khatam An-Nubuwwa" (The Seal of Prophethood) between his shoulders like a button of a tent. (Volume 7, Book 70, Number 574)