Surah 28. Al-Qasas, Ayah 17

According to Ibn 'Abbas and Muqatil (both of them quoted by Baghawi), "this is an indication that the Israelite whom Moses had helped was a denier of the truth (kafir)" - i.e., in the moral sense of this definition. (See also last sentence of verse {86} of this surah.)

He takes a conscious and solemn vow to dedicate himself to Allah, and to do nothing that may in any way assist those who were doing wrong. This was his general idea, but no plan had yet shaped itself in his mind, until a second catastrophe brought matters to a head, and he was plunged in adventure.