Sayyiduna Abu Ayyub (may Allah be pleased with him) said: I heard the Prophet of Allah (peace and blessings be upon him) say: "No prophet was sent, nor was there any caliph after him, except that he had two close circles: a circle that commands him to do good and forbids him from evil, and a circle that spares no effort in ruining him. So whoever is protected from the evil circle has been protected (from harm)."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3880