Truly, when it was said to them: La ilaha ill-Allah "(none has

﴿إِنَّهُمۡ كَانُوٓاْ إِذَا قِيلَ لَهُمۡ لَآ إِلَٰهَ إِلَّا ٱللَّهُ يَسۡتَكۡبِرُونَ ﴾
[الصَّافَات: 35]

Truly, when it was said to them: La ilaha ill-Allah "(none has the right to be worshipped but Allah)," they puffed themselves up with pride (i.e. denied it)

﴿إنهم كانوا إذا قيل لهم لا إله إلا الله يستكبرون﴾ [الصَّافَات: 35]

Al Bilal Muhammad Et Al
For they, when they were told that there is no god except God, would puff themselves up with pride–

Ali Bakhtiari Nejad
Indeed when it was said to them there is no god except God, they were arrogant

Ali Quli Qarai
Indeed, it was they who, when they were told, ‘There is no god except Allah,’ used to be disdainful

Ali Unal
For when they were told that there is no deity but God, they would grow arrogant and reject it

Hamid S Aziz
Surely they used to behave arrogantly when it was said to them, "There is no God but Allah

John Medows Rodwell
Because when it was said to them, There is no God but God, they swelled with pride

Literal
That they truly were if (it) was said to them: "No God except god" they be arrogant

Mir Anees Original
When it was said to them, “There is no god except Allah,” they certainly used to consider themselves great (to accept this)

Mir Aneesuddin
When it was said to them, “There is no god except God,” they certainly used to consider themselves great (to accept this)