Musannaf Ibn Abi Shayba 18:1290

Abu Bakr narrated to us, he said: Abu Khalid narrated to us, from Ash'ath, from Fudayl, from Abdullah ibn Ma'qil, who said: I was sitting with Ali when a man came to him and whispered to him. Ali said: "O Qanbar!" The people said: "O Qanbar!" He said: "Take this one out and flog him." Then the flogged man came and said: "He has exceeded [the limit] against me by three lashes." Ali said: "What do you say?" He said: "He spoke the truth, O Commander of the Faithful." He said: "Take the whip and flog him three lashes." Then he said: "O Qanbar, when you flog, do not exceed the limits."