Shahadah is the first pillar of Islam. A Muslim declares or affirms his faith by reciting:
“I declare that there is no god but Allah and I declare that Muhammad is the Messenger of Allah”
This declaration is called al-Kalimatut Taiyibah. It contains the whole of Islamic belief. There are two parts. The first part is about the Oneness of Allah (called Tawhid) while the second part concerns the prophethood (Risalah) of Muhammad (peace and blessing be upon him).
While the first pillar in Islam is around Tawhid and Risalah, the remaining four pillars are the main duties in Islam.