Musannaf Ibn Abi Shayba 27:404

Hussayn ibn Ali narrated to us, from Za'idah, from Abu Hasin, from Sa'id ibn Ubaydah, who said: A man asked Ibn Umar about Uthman, so he mentioned his best deeds. Then he said, "Perhaps that displeases you?" He replied, "Yes." He said, "May Allah rub your nose in the dust."