Musannaf Ibn Abi Shayba 37:278

Yazid ibn Harun narrated to us, he said: Ibn 'Awn informed us, from Muhammad, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him), who said: "The angels curse one of you if he points at his brother with a piece of iron, even if he is his brother through his father and mother."