The Fire Worshipper Meets Hazrat Junaid e Baghdadi Radi Allahu Anhu)

Once a Majoosi (fire worshipper) put on a Zanaar (a so-called sacred thread worn by fire worshippers), and then disguised himself as a Muslim, by putting on the Arabian garb. He then presented himself before Hazrat Junaid-e-Baghdadi and said, "I have come to ask the meaning of a Hadith Shareef, which says, "Itaqu bi firaasatil Mo'min Fa In'nahu yanzuroo bi Nooril'laahi" (Fear of the sight of a true believer, for he sees with the Noori of Allah). "Could you explain the meaning of this Hadith?" Hazrat Junaid-e-Baghdadi heard his questioned and smiled. He said, "It means that you should break your zanaar, leave kufr and accept Islam." When he heard Hazrat's reply, he was astonished, and immediately recited the Kalima Shareef and accepted Islam. 

(Radi Allahu Anhu)

[Tazkiratul Awliyah pg.233]