Shama-il Tirmidhi Chapter 2, Hadith Number 2 (16).

Jaabir bin Samurah (Radhiallahu Anhu reports that: “I saw the Seal of Prophethood of Rasullullah (Sallallahu alaihi wasallam) between his two shoulders, which was like a red tumor (protruding flesh), the size of which was like that of a pigeon’s egg”.

Commentary.
There are various and different narrations regarding the size and colour of the Seal of Prophethood of Sayyidina Rasullullah (Sallallahu alaihi wasallam). Qurtubi has reconciled these by saying that the size changed from time to time, as did the colour. According to this humble servant, this reconciliation may also be possible, that in reality all these are similarities, and every similarity is according to a person’s understanding, which is an approximate state. There is no disagreement in explaining approximates. This is a more appropriate explanation.