Musannaf Ibn Abi Shayba 19:754

Abu Bakr narrated to us, he said: Hushaym narrated to us, from Mughira, from al-Sha’bi, that the Jews said to the Prophet, peace be upon him: "What is the limit for that?"—meaning stoning. He said: "If four [witnesses] testify that they saw him entering as the kohl applicator enters the kohl container, then stoning has become mandatory."