The uṣūl al-dīn are the foundations of the Muslim belief system. After the shahāda, they are the basic theological foundations of Islam which a Muslim must believe in. They are five: 

The first is Tawhīd or the Absolute Oneness and Unity of God, meaning that Allah is the Only Creator and Sustainer of all of existence and that He has no partners in anything He does. It also means that He is the only One worthy of worship to the exclusion of all other things. All other beliefs in Islam are predicated on the notion of tawhīd. 

The second principal is that of ʿadālah, or Divine Justice. This means that God is absolutely good and just and He does not command or act unjustly towards His creation. 

The third principal is Nubuwwa or Prophethood. As a Just God, Allah sent Prophets to humankind in order to guide them to salvation. The most important and final Prophet is the Prophet Muhammad (s).  

The fourth principal is Imāmah or Divine Leadership. As the Prophet Muhammad (s) is the final Prophet, and Islam is the final religion, we need divinely guided leaders to protect the message and interpretation of Islam. These divine leaders or Imāms are 12 in number and are from the Holy Household of the Prophet (s). 

The fifth principal is Maʿād or resurrection on the Day of Judgment. As the God wants the best for humankind, He sends Prophets to warn them about a Day of Judgment in which they will be accountable for their deeds.