وَإِذْ نَجَّيْنَاكُم مِّنْ آلِ فِرْعَوْنَ يَسُومُونَكُمْ سُوءَ الْعَذَابِ يُذَبِّحُونَ أَبْنَاءَكُمْ وَيَسْتَحْيُونَ نِسَاءَكُمْ ۚ وَفِي ذَٰلِكُم بَلَاءٌ مِّن رَّبِّكُمْ عَظِيمٌ
Wa iz najjaynaakum min aali Fir'awna yasoomoonakum sooo'al 'azaabi yuzabbihoona abnaa'akum wa yastahyoona nisaa'akum; wa fee zaalikum balaa'um mir Rabbikum 'azeem
And remember when we delivered you from the people of Pharaoh, who afflicted you with the worst torment — slaughtering your sons and sparing your women. In that was a tremendous trial from your Lord.
Sāma, the verb behind the affliction, is used of driving livestock to pasture, so what it describes is relentless and daily rather than a single blow. Balā' then names the whole thing a trial, and the root gives both testing and blessing in Arabic, which is why commentators disagreed over whether the trial named is the oppression or the rescue from it.