Musannaf Ibn Abi Shayba 21:429

Abu Usama narrated to us, from Mis'ar, from 'Amr ibn Qays, from 'Amr ibn Abi Qurra, from Salman, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I am from the children of Adam. So, whichever servant of my nation I have cursed with a curse or insulted with an insult, while he did not deserve it, then make it a prayer (blessing) for him."