At-Tusi is not certain that Harut and Marut are infallible

Muhammad Ibn Hasan At-Tusi writes:

أًمَّـا الـرِّوَايَـاتُ الَّـتِـي فِـي أَنَّ الْـمَـلَـكَـيْـنِ أَخْـطَـأَآ وَرَكِـبَـا الْـفَـوَاحِـشَ فَـإِنَّـهَـا أَخْـبَـارُ آحَـادٍ مَـنِ اعْـتَـقَـدَ عِـصْـمَـةَ الْـمَـلَائِـكَـةِ يَـقْـطَـعُ عَـلَـى كِـذْبِـهَـا وَمَـنْ لَـمْ يَـقْـطَـعْ عَـلَـى ذَلِـكَ جَـوَّزَ أَنْ تَـكُـونَ صَـحِـيـحَـةً وَلَا يَـقْـطَـعُ عَـلَـى بُـطْـلَانِـهَـا وَالَّـذِي نَـقُـولُـهُ إِنْ كَـانَ الْـمَـلَـكَـانِ رَسُـولَـيْـنِ فَـلَا يَـجُـوزُ عَـلَـيْـهِـمَـا ذَلِـكَ وَإِنْ لَـمْ يَـكُـونَـا رَسُـولَـيْـنِ جَـازَ ذَلِـكَ وَإِنْ لَـمْ نَـقْـطَـعْ بِـهِ

“As for the traditions that say that the two angels (2:102) committed errors and committed shameful acts, these are only individual reports (Ahad). Those who believe in the infallibility of the angels are certain that these are lies, and those who are not certain about this are certain that these are true and are not certain that these are false, and what we are saying is that if the two angels are messengers, it is not permissible for them to be so, but if the two are not messengers, it is permissible, although we are not certain about this.” [At-Tibyan, Volume 1, Page 384]