Musannaf Ibn Abi Shayba 13:2135

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sufyan narrated to us, from ‘Asim ibn Abi al-Najud, from Zirr ibn Hubaysh, from Ibn Mas’ud, he said: Al-suht (illicit gain) is bribery.