Prophet Muhammad has said in Hadith that your slave is your brother. He used to treat his own slaves as his sons. When he migrated to Madina from Mecca, he ordered his slave to sit in the camel,and he himself was holding the rein and walking in the desert as he believed that the slave should also take some rest.When the people of Madina approached ,they mistook the slave as prophet and dismounted him from the camel with respect and fun fare. Later only they realised that the man walking beside the camel is actually the prophet of Islam. Such was the humility of the prophet.
