Musannaf Ibn Abi Shayba 19:751

Abu Bakr narrated to us, he said: Yahya ibn Adam narrated to us, he said: Hammad ibn Zayd narrated to us, from Yahya ibn Atiq, from Ibn Sirin, that some people testified against a man regarding adultery. He said: So Uthman said with his hand like this, "Do you testify that he...?" and he began to insert his index finger into his left finger, having bent it into a ten.