Surah 43. Az-Zukhruf, Ayah 52

An allusion to the impediment in speech from which Moses suffered (cf. {20:27-28} and the corresponding note [17]), or perhaps to the contents of his message, which to Pharaoh appeared unconvincing.

 Moses used to have a speech impediment. But when he became a prophet he prayed to Allah to help him speak clearly, and his prayer was answered (see 20:25-36).

Being a despised Israelite in any case, and having further an impediment in his speech. See xx. 27, and notes 2552-53.