Musannaf Ibn Abi Shayba 19:296

Abu Bakr narrated to us, he said: Abda narrated to us, from Muhammad ibn Ishaq, he said: Al-Qasim was asked about a man who says to a man, "O son of the tailor," or "O son of the cupper," or "O son of the butcher," while his father is not like that. Al-Qasim said: "We have reached [a time/people], and the prescribed punishments (hudud) are not established except in clear accusation of unchastity (qadhf) or in clear denial of lineage (nafi)."