Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) returned from Khaybar and with him were two slaves. Sayyiduna Ali (may Allah be pleased with him) said to him: O Messenger of Allah! Give us one of the slaves. The Prophet (peace and blessings of Allah be upon him) said: "Take whichever one you wish." He said: You choose for me. The Prophet (peace and blessings of Allah be upon him) said: "Take this one, but do not kill him, for I saw him performing prayer on the way back from Khaybar, and I have been forbidden to kill those who pray." The Prophet (peace and blessings of Allah be upon him) gave the other slave to Sayyiduna Abu Dharr (may Allah be pleased with him) and instructed him to treat him with goodness and kindness. Then one day he asked: "Abu Dharr! What happened to the slave I gave you?" He replied: You instructed me to treat him with goodness and kindness, so I set him free.