Musnad Ahmad 4010

It was narrated from al-Aizar from Tin'ah, that Ibn Mas’ood said: I heard the Messenger of Allah (ﷺ) say: “If a curse is directed at someone, it goes in his direction, then if it finds a way to reach him it befalls him, otherwise it will turn to its Lord and say: "O Lord, So and so directed me at So and so, but I could not find any way to reach him, What do You instruct me to do?" And He will say: 'Go back from whence you came."