Niyyah
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Niyyah is an intent one evokes in his heart to do an act of worship for the sake of Allah (God). Thus, because its seat is in the heart, it does not have to be pronounced verbally. That is why no wording for Niyyah is reported from the Prophet (s.a.s.), nor from any of his companions.
Taken from "The Prescribed Prayer Made Simple" by Tajuddin B. Shu'aib