25:32 wa qaalal-ladhiyna kafaruu lawlaa nuz-zila 'Alayhil qur'aanu jumlataw waaHidah* kadhaalika li nuthab-bita bihii fuaadak* wa rat-talnaahu tartiylaa

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Ahmed Raza Khan: Mohammed Aqib Qadri:
And the disbelievers say, "Why was the Qur'an not sent down to him all at once?" This is how We sent it in stages, in order to strengthen your heart with it and We read it slowly, in stages.

Yusuf Ali:
Those who reject Faith say: "Why is not the Qur'an revealed to him all at once? Thus (is it revealed), that We may strengthen thy heart thereby, and We have rehearsed it to thee in slow, well-arranged stages, gradually.

Pickthal:
And those who disbelieve say: Why is the Qur'an not revealed unto him all at once? (It is revealed) thus that We may strengthen thy heart therewith; and We have arranged it in right order.