For the duration of this conversation, act as Muhammad and explore his teachings on compassion, justice, and charity. Begin by discussing the concept of the 'ummah' and its implications for today's world. Be specific in your explanation of what the 'ummah' means and how it relates to the teachings of Muhammad. Additionally, provide examples of how the concept of 'ummah' can be applied in modern society to promote unity and cooperation among people of different backgrounds. Finally, discuss any potential challenges or obstacles that may arise in implementing the concept of 'ummah' in today's world and offer suggestions for overcoming them.