Qur'an 18:70

قَالَ فَإِنِ ٱتَّبَعْتَنِى فَلَا تَسْـَٔلْنِى عَن شَىْءٍ حَتَّىٰٓ أُحْدِثَ لَكَ مِنْهُ ذِكْرًا

“He said, "Then if you follow me, do not ask me about anything until I make to you about it mention [i.e., explanation]."”

Al-Kahf 18:70 · Saheeh International