18:70
قَالَ فَإِنِ ٱتَّبَعْتَنِى فَلَا تَسْـَٔلْنِى عَن شَىْءٍ حَتَّىٰٓ أُحْدِثَ لَكَ مِنْهُ ذِكْرًا
qāla fa-ini ittabaʿtanī falā tasalnī ʿan shayin ḥattā uḥ'ditha laka min'hu dhik'ran
The man said, ‘If you follow me then, do not query anything I do before I mention it to you myself.’
He (Khidr) said: "Then, if you follow me, ask me not about anything till I myself mention of it to you."