Musannaf Ibn Abi Shaybah 24528 — What a witness should not speak of

It is narrated from al-Ja'd bin Dhakwan that a man came forward before Shurayh and called for a witness of his, saying: "Where is Rabi'ah al-Kuwayfir (the little unbeliever)?" He came, and Shurayh said: "You have admitted to 'Kuwayfir' (little unbeliever)." Then he rejected his testimony.