Abu Umama reported,

The Messenger of Allah ﷺ came back from Khaybar with two young servants. Ali said, "Messenger of Allah, give us a servant to help us."He replied, "Take whichever of them you wish."Ali said, "Choose one for me."He said, "Take this one, and do not strike him, for I saw him praying as we were on our way back from Khaybar, and I have been forbidden from striking those who pray."He gave the other boy to Abu Dharr and said, "Treat him well."Later he asked, "Abu Dharr, what did you do with the boy I gave you?"Abu Dharr replied, "You instructed me to treat him well, so I set him free."

حدثنا عفان حدثنا حماد بن سلمة أخبرنا أبو غالب

عن أبي أمامة

أن رسول الله ﷺ أقبل من خيبر ومعه غلامان فقال علي رضي الله عنه يا رسول الله أخدمنا فقال خذ أيهما شئت فقال خر لي قال خذ هذا ولا تضربه فإني قد رأيته يصلي مقبلنا من خيبر وإني قد نهيت عن ضرب أهل الصلاة وأعطى أبا ذر الغلام الآخر فقال استوص به خيرا ثم قال يا أبا ذر ما فعل الغلام الذي أعطيتك قال أمرتني أن أستوصي به خيرا فأعتقته