Qur'ān 36:11 · Ya-Sin (يس)

إِنَّمَا تُنذِرُ مَنِ ٱتَّبَعَ ٱلذِّكْرَ وَخَشِىَ ٱلرَّحْمَـٰنَ بِٱلْغَيْبِ ۖ فَبَشِّرْهُ بِمَغْفِرَةٍۢ وَأَجْرٍۢ كَرِيمٍ

You can only warn one who follows the message and fears the Most Merciful unseen. So give him good tidings of forgiveness and noble reward.