Is it permissible to say that the Companions erred?

The error attributed to the entire body of Companions is null and void, due to the Prophet's (peace be upon him) saying: "Indeed, Allah will not gather my Ummah upon misguidance." The Companions are the most deserving of this Hadith. However, deeming one of them or some of them mistaken is acceptable, because the Ahl al-Sunnah (Sunnis) have unanimously agreed that they are human beings who are not infallible. Yet, their lack of infallibility does not undermine their uprightness. One should consider the intent of whoever deems one of them mistaken. If the purpose is to negate infallibility from individuals among them, then it is true. But if it is taken as a means to revile them and defame them, then it is among the signs of the people of discord and hypocrisy.