There was a battle against Jews in Khaybar. A black person who was working as a shepherd there decided to become a Muslim. He went over to Hazrat Muhammad (pbuh) and told him about it. However, Hazrat Muhammad (pbuh) did not accept his wish first; he said to the shepherd,

"First, you need to give the herd to its owner. The fact that you want to be a Muslim and join the battle with us will not eliminate the responsibility of the things entrusted to you."

The shepherd did as he was told. He returned the herd to its owner and then acted in accordance with the obligations of his new religion.