وَإِذْ قُلْتُمْ يَا مُوسَىٰ لَن نُّؤْمِنَ لَكَ حَتَّىٰ نَرَى اللَّهَ جَهْرَةً فَأَخَذَتْكُمُ الصَّاعِقَةُ وَأَنتُمْ تَنظُرُونَ
Wa iz qultum yaa Moosaa lan nu'mina laka hattaa naral laaha jahratan fa akhazatkumus saa'iqatu wa antum tanzuroon
And remember when you said, "Musa, we will not believe you until we see God plainly" — and the thunderbolt seized you as you looked on.
Jahratan means openly, in plain and unmediated sight, and the demand it qualifies is for perception without any intermediary. Musa himself asks something close to this later in the Qur'an and receives an answer about the mountain rather than a refusal. Here the request comes from those who have already been shown a sea divided, which is what makes the demand a matter of terms rather than evidence.