صحيح البخاري

Narrated As-Sa'ib bin Yazid:

My aunt took me to the Prophet (ﷺ) and said, "O Allah's Messenger! 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.)