It is narrated from Hazrat Jabir bin Samurah (may Allah be pleased with him) that I saw the Seal of Prophethood on the blessed back of the Prophet (peace and blessings be upon him); it was the size of a pigeon’s egg.
Hadith Referenceمسند احمد / أول مسند البصريين / 20934
Hadith Gradingحکم دارالسلام:حديث حسن، وهذا إسناد ضعيف، يحيى بن عبدالله ضعيف