(Asshuara’) 26 : 13
وَيَضِيقُ صَدْرِي وَلَا يَنْطَلِقُ لِسَانِي فَأَرْسِلْ إِلَىٰ هَارُونَ
“And that my chest is narrowed and my tongue is not fluent, so You send to Haroon”.
See explanation 20: 25-35.