Sayyiduna Ali (may Allah be pleased with him) said: A man came to the Prophet (peace and blessings be upon him) so that he would take his pledge of allegiance, and there was a trace of khaluq on him, so the Prophet (peace and blessings be upon him) refused to take his pledge. The man went and washed the trace of khaluq off himself, then he came, and the Prophet (peace and blessings be upon him) then took his pledge.
Al-Bazzar recorded it from his teacher Abdullah bin al-Muthanna al-Taymi, whom I do not know. The remaining narrators of this report are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب اللباس / 8754