It was narrated that 'Ali said:
"The Messenger of Allah (ﷺ) said: 'No slave truly believes until he believes in four things: in Allah alone with no partner; that I am the Messenger of Allah; in the resurrection after death; and in the Divine Decree (Qadar).'" (ID)
English reference (ID): Vol. 1, Book 1, Hadith 81 (ID)
Arabic reference (ID): Book 1, Hadith 85 (ID)