Musnad Ahmad 1099:2

Abdullah narrated to us, my father narrated to me, from his book: Ibrahim ibn Khalid narrated to us, Rabah ibn Zayd narrated to us, Umar ibn Habib narrated to me, from Abdullah ibn Uthman ibn Khuthaym, who said: I entered upon Abu al-Tufayl and found him in good spirits. I said, "I shall take advantage of this from him." So I said, "O Abu al-Tufayl, the group whom the Messenger of Allah, peace and blessings of Allah be upon him, cursed—among them—who are they?" He intended to tell me about them, but a black woman said to him, "Desist, O Abu al-Tufayl. Has it not reached you that the Messenger of Allah, peace and blessings of Allah be upon him, said: 'O Allah, I am only a human being, so whichever servant of the believers I have invoked a curse upon, make it for him a purification and a mercy'?"