Surah Ash-Shu'ara 26:13

وَيَضِيقُ صَدْرِى وَلَا يَنطَلِقُ لِسَانِى فَأَرْسِلْ إِلَىٰ هَـٰرُونَ

And that my breast will tighten and my tongue will not be fluent, so send for Aaron.

Translation: Saheeh International

Tafsir

and that anguish will constrain my breast because of their denial of me and that my tongue will not utter clearly to deliver the Message because of the knot in it. So give the Mission to my brother Aaron alongside me.

Excerpt from Tafsir al-Jalalayn, commentary on 26:13, via Quran.com. The reader has the full commentary and 9 more tafsirs.