The word(s) "harden" appears 4 time(s) in 4 verse(s) in Quran in Muhammad Habib Shakir translation.

(1) Then your hearts hardened after that, so that they were like rocks, rather worse in hardness; and surely there are some rocks from which streams burst forth, and surely there are some of them which split asunder so water issues out of them, and surely there are some of them which fall down for fear of Allah, and Allah is not at all heedless of what you do.

(2) Yet why did they not, when Our punishment came to them, humble themselves? But their hearts hardened and the Shaitan made what they did fair-seeming to them.

(3) And Musa said: Our Lord! surely Thou hast given to Firon and his chiefs finery and riches in this world's life, to this end, our Lord, that they lead (people) astray from Thy way: Our Lord! destroy their riches and harden their hearts so that they believe not until they see the painful punishment.

(4) Has not the time yet come for those who believe that their hearts should be humble for the remembrance of Allah and what has come down of the truth? And that they should not be like those who were given the Book before, but the time became prolonged to them, so their hearts hardened, and most of them are transgressors.