Musannaf Ibn Abi Shayba 26:512

Waki' narrated to us, he said: Isra'il narrated to us, from Jabir, from 'Amir, from Shurayh, that he used to not judge by the dragging of *al-wala'* (patronage/clientage) until al-Aswad narrated to him from 'Abdullah that he had judged by it, so Shurayh judged by it.