Sumama was the leader of his city. He hated the Prophet Muhammad (pbuh) and he did everything in his power to harm him. He used to talk very negative about our Prophet (pbuh). He was found in Mecca and the companions caught him and brought him in front of the Prophet (pbuh). What would you do in this situation? Your enemy is right in front of you.
The Prophet told them to tie him up in the masjid and be kind to him, take care of him, give him good food. Sumama heard the Quran being read in the salat, he watched all of the Prophets interactions with the Companions.
The Prophet went to him and asked “What should I do with you?” Sumama said “If you kill me know there will be war between my people and yours, if you free me I will be very thankful and if you need money just tell me a price”.
The Prophet (pbuh) came back to him 3 different times and Sumama gave him the same answers. The Prophet then decided to free him. This is the Mercy the Prophet Muhammad was to mankind!
A little while later Sumama went back to the masjid and said “I bear witness there is no God but Allah and that Muhammad is the messenger of Allah”.