Unless Allah wills, none on this earth can harm me

It is narrated from Imam Ja’far As-Sadiq (as) that Amir’ul-Mu’mineen ‘Ali (as) had lot of affection for his slave Qanbar (r.a.). When Amir’ul-Mu’mineen ‘Ali (as) went out, Qanbar (r.a.) used to carry a sword in his hand as a measure of protection for his master. One moonlit night Amir’ul-Mu’mineen ‘Ali (as) emerged from his residence. On the way he noticed that Qanbar (r.a.), as usual, was following him. He asked, “Qanbar! Why have you come?” Qanbar (r.a.) said, “I have come, lest someone harm you!” Amir’ul-Mu’mineen ‘Ali (as) asked him, “Do you intend to protect me from the creatures of the other world or from those on the earth?” Qanbar said, “I can protect you from the creatures that are on the earth!” Amir’ul-Mu’mineen ‘Ali said, “Unless Allah wills, none on this earth can harm me. Go back home in peace!” Qanbar (r.a.) went back home as ordered by his master. Reference :Ain-Al Hayat, The Essence of Life