Sayyiduna Miswar bin Makhramah (may Allah be pleased with him) narrates: A Jew passed by me while I was behind the Prophet (peace and blessings be upon him), and the Prophet (peace and blessings be upon him) was performing ablution (wudu). His (peace and blessings be upon him) garment shifted from his (peace and blessings be upon him) back, and the Seal of Prophethood could be seen on his (peace and blessings be upon him) back. The Jew said: "Lift his garment back up over his back." So I began to lift the garment of the Prophet (peace and blessings be upon him) over his (peace and blessings be upon him) back, and the Prophet (peace and blessings be upon him) splashed a handful of water on my face.
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17168