Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) narrates: The people said: O Messenger of Allah! How will you (peace and blessings be upon him) recognise those members of your Ummah whom you (peace and blessings be upon him) have not seen? The Prophet (peace and blessings be upon him) said: They will be radiant and shining (with bright foreheads) because of ablution.
Imam al-Tabarani recorded this report in al-Mu'jam al-Awsat; its chain contains a narrator, Hasan bin Husayn al-Arabi, and he is extremely da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الطهارة / 1141