From Sahih Muslim (Hadith 6087):
As-Sa'ib b. Yazid reported:My mother's sister took me to Allah's Messenger (ﷺ) and said: Allah's Messenger, here is the son of my sister and he is ailing. He touched my head and invoked blessings upon me. He then performed ablution and I drank the water left from his ablution; then I stood behind him and I saw the seal between his shoulders
Reference: Muslim 6087