At-Tusi confirms that the devil was one of the angels

Muhammad Ibn Hasan At-Tusi writes:

مَـسْـأَلَـةٌ عَـنْ إِبْـلِـيـسَ لَـعَـنَـهُ اللهُ مَـا الَّـذِي أَلْـزَمَـهَ الـسُّـجُـودُ لِآدَمَ وَالْأَمْـرُ بِـذَلِـكَ إِنَّـمَـا تَـوَجَّـهَ إِلَـى الْـمَـلَائِـكَـةِ وَلَـيْـسَ مِـنْ قَـبِـيـلِـهِـمْ فِـي شَـيْءٍ. الْـجَـوَابُ: ظَـاهِـرُ مَـذْهَـبِ أَصْـحَـابِـنَـا أَنَّ إِبْـلِـيـسَ كَـانَ مِـنْ جُـمْـلَـةِ الْـمَـلَائِـكَـةِ وَإِنَّـمَـا عَـصَـى بِـتَـرْكِ الـسُّـجُـودِ وَلَـيْـسَ جَـمِـيـعُ الْـمَـلَائِـكَـةِ مَـعْـصُـومِـيـنَ بَـلْ نَـقْـطَـعُ عَـلَـى أَنَّ الـرُّسُـلَ مِـنْـهُـمْ كَـذَلِـكَ وَالْـبَـاقِـي يَـجُـوزُ عَـلَـيْـهِـمُ الْـخَـطَـأُ وَهُـوَ مَـذْهَـبُ كَـثِـيـرٍ مِـنَ الْـمُـفَـسِّـرِيـنَ وَالْـعُـلَـمَـاءِ

“A question for the devil, May God curse him: “Why did he have to bow down before Adam, when the command was only addressed to the angels and he had nothing at all to do with their affair?” Answer: “The belief of our companions obviously says that the devil belonged to the angels (38:73) and he only disobeyed by refraining from prostration (38:74) and not all angels are infallible, but we are certain that it is the messengers among them and as for the rest, it is quite possible for them to make mistakes and the majority of exegetes and scholars believe in this.” [Ar-Rasa’il-ul-Ashar, pages 327 – 328]