Musannaf Ibn Abi Shayba 4:825

Sufyan ibn 'Uyaynah narrated to us, from 'Ammar, from 'Abdullah ibn Yasar, from his father, that 'Ali aided Ja'dah ibn Hubayrah with seven hundred dirhams from his stipend for the price of a servant. Then he asked him, "Have you purchased a servant?" He replied, "I am in i'tikaf (seclusion in the mosque)." He said, "And what is upon you if you went to the market and purchased a servant?"