It is narrated from Sayyiduna Zayd bin Arqam (may Allah be pleased with him); he said: A man from the Jews cast magic on the Prophet (peace and blessings be upon him), because of which he (peace and blessings be upon him) remained ill for several days. Then Jibril (peace be upon him) came to him (peace and blessings be upon him) and said: "A man from the Jews has cast magic on you; he has tied some knots against you." So the Messenger of Allah (peace and blessings be upon him) sent Sayyiduna Ali (may Allah be pleased with him) for it, and he took out those knots and brought them. Each time he (peace and blessings be upon him) untied a knot, he felt that much lighter, until the Prophet (peace and blessings be upon him) stood up as though he had been released from a tether. After that the Prophet (peace and blessings be upon him) never mentioned that Jew, nor did he (the Jew) ever see any (trace) of it in his (peace and blessings be upon him) face.
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4997