What is the difference between sincerity (ikhlas) and intention (niyyah)?

Sincerity (Ikhlas) is the act of dedicating one's deeds solely to Allah Almighty, purifying them from any impurities. Intention (Niyyah), on the other hand, is the resolve of the heart and the purpose behind an action. It is what distinguishes between different types of worship. Sometimes, the term "niyyah" is used to mean both sincerity and purpose.

Ibn Rajab explained that the term "niyyah" in the discourse of scholars carries two meanings: The first is to distinguish between different acts of worship, or to distinguish acts of worship from customary actions. This meaning is found in the writings of jurists (fuqaha'). The second is to distinguish the ultimate purpose of an action, whether it is solely for Allah or for someone else. This is the sincerity (ikhlas) that the Gnostics (Aarifun) speak of, and it is found in the discourse of the Salaf. Sometimes, both meanings are expressed by the terms "iradah" (will/desire) and "ibtigha'" (seeking/desiring). Thus, it becomes clear that intention (niyyah) is broader than sincerity (ikhlas).