Jami` at-Tirmidhi Book 49, Hadith 39

"My maternal aunt took me to the Prophet (ﷺ), and said: 'O Messenger of Allah! Indeed my nephew is in pain.' So he wiped over my head and supplicated for blessings for me. And he performed Wudu and I drank from the water of his Wudu. Then I stood behind his back, and I looked at the seal between his two shoulder blades, and it resembled the egg of a partridge.

Previous Hadith

"The laughter of the Messenger of Allah (ﷺ) was not but smiling."

Jami` at-Tirmidhi Book 49, Hadith 38
Next Hadith

"The seal of the Messenger of Allah (ﷺ)" - meaning the one which was between his two shoulder blades - "was fleshy and red, resembling the egg of a pigeon."

Jami` at-Tirmidhi Book 49, Hadith 40