Ibn Hibban

Ubaid bin Ya'la reports: We participated in a battle with Abdur Rahman bin Khalid bin Walid. There, four camels were brought along with the enemy, so under the order of Abdur Rahman bin Khalid, they were tied up and killed with spears. When this was reported to Sayyiduna Abu Ayyub Ansari (may Allah be pleased with him), he said: I heard the Prophet Muhammad (peace be upon him) forbidding killing while tied up. By Him in Whose hand is my soul, even if it were a chicken, I would not use it for target practice while tied up. When this was reported to Abdur Rahman bin Khalid, he freed four slaves.