Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
quran:26:13 –

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

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.
القرآن:٢٦:١٣ –

وَيَضِيقُ صَدْرِي وَلَا يَنْطَلِقُ لِسَانِي فَأَرْسِلْ إِلَىٰ هَارُونَ  

{ويضيق صدري} من تكذيبهم لي {ولا ينطلق لساني} بأداء الرسالة للعقدة التي فيه {فأرسل إلى} أخي {هارون} معي.