Musnad Ahmad 26:486

Ya'la narrated to us, Umar ibn Dharr narrated to us, from al-Aizar, from Tan'ah, that Ibn Mas'ud said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: "When a curse is directed, it heads toward the one it was directed at. If it finds a path in him and finds a way upon him, it settles upon him. Otherwise, it returns to its Lord and says: 'O Lord, such-and-such person directed me toward such-and-such person, and I did not find a way upon him, nor did I find a path in him. So what do You command me?' He says: 'Return from where you came.'"