The word(s) "hardened" appears 4 time(s) in 4 verse(s) in Quran in Abdullah Yusuf Ali translation.

(1) Thenceforth were your hearts hardened: They became like a rock and even worse in hardness. For among rocks there are some from which rivers gush forth; others there are which when split asunder send forth water; and others which sink for fear of Allah. And Allah is not unmindful of what ye do.

(2) When the suffering reached them from us, why then did they not learn humility? On the contrary their hearts became hardened, and Satan made their (sinful) acts seem alluring to them.

(3) That He may make the suggestions thrown in by Satan, but a trial for those in whose hearts is a disease and who are hardened of heart: verily the wrong-doers are in a schism far (from the Truth):

(4) Is one whose heart Allah has opened to Islam, so that he has received Enlightenment from Allah, (no better than one hard-hearted)? Woe to those whose hearts are hardened against celebrating the praises of Allah! they are manifestly wandering (in error)!